public static void main(String[] args) throws IOException {
Scanner scanner = new Scanner(new BufferedInputStream(System.in));
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
while (true) {
int a = Integer.parseInt(br.readLine());
if (a == 0) break;
HashMap<String, Integer> map = new HashMap<String, Integer>();
int sum = 0;
while (a-- > 0) {
StringTokenizer st = new StringTokenizer(br.readLine());
int one = Integer.parseInt(st.nextToken()), two = Integer.parseInt(st.nextToken());
country c = new country(one, two);
country c_rev = new country(two, one);
int s = 0;
if (map.get(c.tostring()) != null) {
s = map.get(c.tostring()) + 1;
map.put(c.tostring(), s);
sum++;
} else if (map.get(c_rev.tostring()) != null) {
s = map.get(c_rev.tostring()) - 1;
map.put(c_rev.tostring(), s);
sum--;
} else {
map.put(c.tostring(), 1);
sum++;
}
}
if (sum != 0) System.out.println("NO");
else System.out.println("YES");
}
}
/**
* Return a set of the variables in the supplied expression. Note: Substitutions which are in the
* constant table are not included.
*/
public Set<String> getVariablesWithin(String exp) {
Set<String> all = new TreeSet<String>(String.CASE_INSENSITIVE_ORDER);
String add = null;
if (separators == null) {
StringBuilder sep = new StringBuilder(10);
for (char chr = 0; chr < operators.length; chr++) {
if (operators[chr] != null && !operators[chr].internal) {
sep.append(chr);
}
}
sep.append("()");
separators = sep.toString();
}
for (StringTokenizer tkz = new StringTokenizer(exp, separators, true); tkz.hasMoreTokens(); ) {
String tkn = tkz.nextToken().trim();
if (tkn.length() != 0 && Character.isLetter(tkn.charAt(0))) {
add = tkn;
} else if (tkn.length() == 1 && tkn.charAt(0) == '(') {
add = null;
} else if (add != null && !constants.containsKey(add)) {
all.add(add);
}
}
if (add != null && !constants.containsKey(add)) {
all.add(add);
}
return all;
}
public static String nextString() throws Exception {
for (; st == null || !st.hasMoreTokens(); ) {
String k1 = in.readLine();
if (k1 == null) return null;
st = new StringTokenizer(k1);
}
return st.nextToken();
}
public String next() {
while (tokenizer == null || !tokenizer.hasMoreTokens()) {
try {
tokenizer = new StringTokenizer(reader.readLine());
} catch (IOException e) {
throw new RuntimeException(e);
}
}
return tokenizer.nextToken();
}
String nextToken() {
while (st == null || !st.hasMoreTokens()) {
try {
st = new StringTokenizer(br.readLine());
} catch (Exception e) {
eof = true;
return "0";
}
}
return st.nextToken();
}
String next() {
while (st == null || !st.hasMoreTokens()) {
try {
st = new StringTokenizer(br.readLine());
} catch (IOException e) {
e.printStackTrace();
}
}
return st.nextToken();
}
public static void readFile() throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer(br.readLine(), " ");
n = Integer.valueOf(st.nextToken());
b = new BigInteger(st.nextToken());
int iCount = 0;
bookHeight = new int[n];
while (iCount < n) {
bookHeight[iCount++] = Integer.valueOf(br.readLine());
}
process();
}
String nextToken() {
while (st == null || !st.hasMoreTokens()) {
try {
st = new StringTokenizer(br.readLine());
} catch (Exception e) {
eof = true;
break;
}
}
String ret = buf;
buf = eof ? "-1" : st.nextToken();
return ret;
}
boolean hasNext() {
while (tokenizer == null || !tokenizer.hasMoreTokens())
try {
tokenizer = new StringTokenizer(buff.readLine());
} catch (Exception e) {
return false;
}
return true;
}
String nextToken() {
if (!createST) {
try {
curLine = readLine();
} catch (Exception e) {
eof = true;
}
return null;
}
while (st == null || !st.hasMoreTokens()) {
try {
curLine = readLine();
st = new StringTokenizer(curLine);
} catch (Exception e) {
eof = true;
break;
}
}
String ret = buf;
buf = eof ? "-1" : st.nextToken();
return ret;
}
public void solve() throws Exception {
String str = in.readLine();
int n = str.length();
int t = Integer.parseInt(in.readLine());
int[][] dp = new int[26][n];
dp[str.charAt(0) - 'a'][0] = 1;
for (int i = 1; i < n; i++) {
for (int j = 0; j < 26; j++) {
if (str.charAt(i) == 'a' + j) {
dp[j][i] = dp[j][i - 1] + 1;
} else {
dp[j][i] = dp[j][i - 1];
}
}
}
while (t-- > 0) {
st = new StringTokenizer(in.readLine());
char a = st.nextToken().toCharArray()[0];
char b = st.nextToken().toCharArray()[0];
int l = parseInt(st.nextToken()) - 1;
int r = parseInt(st.nextToken()) - 1;
int ans = 0;
for (int i = l; i <= r; i++) {
if (str.charAt(i) == a) {
ans += dp[b - 'a'][r] - dp[b - 'a'][i];
}
}
out.println(ans);
}
}
public static void main(String[] args) throws Exception {
BufferedReader st = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer s;
s = new StringTokenizer(st.readLine());
int n = Integer.parseInt(s.nextToken());
int r = Integer.parseInt(s.nextToken()) - 1;
visited = new int[n];
int i, a, b;
for (i = 0; i < n; i++) {
adjList.add(new ArrayList<Integer>());
}
for (i = 0; i < n - 1; i++) {
s = new StringTokenizer(st.readLine());
a = Integer.parseInt(s.nextToken());
b = Integer.parseInt(s.nextToken());
adjList.get(a - 1).add(b - 1);
adjList.get(b - 1).add(a - 1);
visited[a - 1] = 0;
visited[b - 1] = 0;
}
dfs(r, 0);
System.out.println(maxh + " " + minh);
}
String next() {
if (!hasNext()) throw new RuntimeException();
return tokenizer.nextToken();
}
String next() throws IOException {
while (!tokenizer.hasMoreTokens()) {
tokenizer = new StringTokenizer(reader.readLine());
}
return tokenizer.nextToken();
}
String next() throws IOException {
while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(in.readLine().trim());
return st.nextToken();
}
private static String nextToken() throws IOException {
while (!tok.hasMoreTokens()) tok = new StringTokenizer(in.readLine());
return tok.nextToken();
}