public class _336_D_Bear_Vasily_and_Beautiful_Strings {
// ->solution screencast http://youtu.be/oHg5SJYRHA0
public void solve() {
int n = ni();
long res = 0;
out.println(res);
}
// IO methods
void run() throws Exception {
long s = System.currentTimeMillis();
solve();
out.flush();
pr(System.currentTimeMillis() - s + "ms");
}
public static void main(String[] args) throws Exception {
new _336_D_Bear_Vasily_and_Beautiful_Strings().run();
}
InputStream in = System.in;
PrintWriter out = new PrintWriter(System.out);
private boolean oj = System.getProperty("ONLINE_JUDGE") != null;
private byte[] inbuf = new byte[1024];
private int lenbuf = 0, ptrbuf = 0;
private int readByte() {
if (lenbuf == -1) throw new InputMismatchException();
if (ptrbuf >= lenbuf) {
ptrbuf = 0;
try {
lenbuf = in.read(inbuf);
} catch (IOException e) {
throw new InputMismatchException();
}
if (lenbuf <= 0) return -1;
}
return inbuf[ptrbuf++];
}
private boolean isSpaceChar(int c) {
return !(c >= 33 && c <= 126);
}
private int skip() {
int b;
while ((b = readByte()) != -1 && isSpaceChar(b)) ;
return b;
}
public String ns() {
int b = skip();
StringBuilder sb = new StringBuilder();
while (!(isSpaceChar(b))) { // when nextLine, (isSpaceChar(b) && b != // ' ')
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
public char[] ns(int n) {
char[] buf = new char[n];
int b = skip(), p = 0;
while (p < n && !(isSpaceChar(b))) {
buf[p++] = (char) b;
b = readByte();
}
return n == p ? buf : Arrays.copyOf(buf, p);
}
public char[][] nm(int n, int m) {
char[][] map = new char[n][];
for (int i = 0; i < n; i++) map[i] = ns(m);
return map;
}
public int[] na(int n) {
int[] a = new int[n];
for (int i = 0; i < n; i++) a[i] = ni();
return a;
}
public int ni() {
int num = 0, b;
boolean minus = false;
while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
if (b == '-') {
minus = true;
b = readByte();
}
while (true) {
if (b >= '0' && b <= '9') {
num = num * 10 + (b - '0');
} else {
return minus ? -num : num;
}
b = readByte();
}
}
public long nl() {
long num = 0;
int b;
boolean minus = false;
while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
if (b == '-') {
minus = true;
b = readByte();
}
while (true) {
if (b >= '0' && b <= '9') {
num = num * 10 + (b - '0');
} else {
return minus ? -num : num;
}
b = readByte();
}
}
void pr(Object... ob) {
if (!oj) System.out.println(Arrays.deepToString(ob).replace("],", "],\n"));
}
}
public class Main6 {
public void solve() {
// Scanner sc = new Scanner(System.in);
// int n = Integer.parseInt(sc.nextLine());
// n = 10000;
pr("\n".getBytes());
int n = ni();
// int xx=100000;
while (n != 0) {
String s = ns1();
// int size = (int)(Math.random()*10000);
// char [] axx = new char[size];
// for (int i = 0; i < axx.length; i++) {
// char ccc = (char)((Math.random()*('z'-'a'))+'a');
//// pr(ccc);
// axx[i]=ccc;
// }
// String s =new String(axx);
// for (int i = 0; i < 1000000; i++) {
// s+='x';
// }
// int[] xa = new int[1000000000];
// pr(s);
int a = 0;
HashMap<Character, Integer> set = new HashMap<Character, Integer>();
// int [] alf= new int[128];
int r = 0;
for (int i = 0; i < s.length(); i++) {
// pr(set);
// char that = s.charAt(a);
char thix = s.charAt(i);
if (set.size() < n) {
Integer ax = set.get(thix);
if (ax == null) {
set.put(thix, 1);
} else set.put(thix, ax + 1);
} else if (set.size() == n) {
if (!set.containsKey(thix)) {
while (set.size() == n && a < s.length()) {
char that = s.charAt(a);
if (set.containsKey(that) && set.get(that) > 1) set.put(that, set.get(that) - 1);
else set.remove(that);
a++;
}
set.put(thix, 1);
} else set.put(thix, set.get(thix) + 1);
}
int newr = i - a + 1;
// pr(newr, set,a,i,s.substring(a,i));
if (newr > r) {
// pr()
// pr(set,a,i,s.substring(a,i));
r = newr;
}
// r=max(r,);
}
out.println(r);
// n = (int)(Math.random()*128);
n = ni();
}
}
void run() throws Exception {
in = oj ? System.in : new ByteArrayInputStream(INPUT.getBytes());
out = new PrintWriter(System.out);
long s = System.currentTimeMillis();
solve();
out.flush();
// pr(System.currentTimeMillis() - s + "ms");
}
public static void main(String[] args) throws Exception {
new Main6().run();
}
InputStream in;
PrintWriter out;
String INPUT = "";
private boolean oj = System.getProperty("ONLINE_JUDGE") != null;
private byte[] inbuf = new byte[1024];
private int lenbuf = 0, ptrbuf = 0;
private int readByte() {
if (lenbuf == -1) throw new InputMismatchException();
if (ptrbuf >= lenbuf) {
ptrbuf = 0;
try {
lenbuf = in.read(inbuf);
} catch (IOException e) {
throw new InputMismatchException();
}
if (lenbuf <= 0) return -1;
}
return inbuf[ptrbuf++];
}
private boolean isSpaceChar(int c) {
return !(c >= 33 && c <= 126);
}
private int skip() {
int b;
while ((b = readByte()) != -1 && isSpaceChar(b)) ;
return b;
}
private String ns() {
int b = skip();
StringBuilder sb = new StringBuilder();
while (!(isSpaceChar(b))) { // when nextLine, (isSpaceChar(b) && b != // ' ')
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
private String ns1() {
int b = skip();
StringBuilder sb = new StringBuilder();
while (!(isSpaceChar(b) && b != ' ')) { // when nextLine,
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
private int[] na(int n) {
int[] a = new int[n];
for (int i = 0; i < n; i++) a[i] = ni();
return a;
}
private int ni() {
int num = 0, b;
boolean minus = false;
while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
if (b == '-') {
minus = true;
b = readByte();
}
while (true) {
if (b >= '0' && b <= '9') {
num = num * 10 + (b - '0');
} else {
return minus ? -num : num;
}
b = readByte();
}
}
private long nl() {
long num = 0;
int b;
boolean minus = false;
while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
if (b == '-') {
minus = true;
b = readByte();
}
while (true) {
if (b >= '0' && b <= '9') {
num = num * 10 + (b - '0');
} else {
return minus ? -num : num;
}
b = readByte();
}
}
void pr(Object... ob) {
if (!oj) System.out.println(Arrays.deepToString(ob).replace("],", "],\n"));
}
}