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");
}
}
public String next() {
while (tokenizer == null || !tokenizer.hasMoreTokens()) {
try {
tokenizer = new StringTokenizer(reader.readLine());
} catch (IOException e) {
throw new RuntimeException(e);
}
}
return tokenizer.nextToken();
}
protected Locale getLocale(HttpServletRequest request) {
String locid = request.getParameter(P_LOCALE_ID);
if (locid == null || locid.length() == 0) {
return request.getLocale();
}
StringTokenizer tokenizer = new StringTokenizer(locid, "_-");
String language = String.valueOf(tokenizer.nextToken()).toLowerCase();
String country = tokenizer.hasMoreTokens() ? tokenizer.nextToken() : null;
if (country != null) {
return new Locale(language, country.toUpperCase());
}
return new Locale(language);
}
/**
* Returns a version of this condition in which the variable names are converted to the names that
* will be used by the java class written to fileText. Instances of "this." are removed. Instances
* of the package and class names prefixing variable names are removed and appended to the
* variable name with a "_" separating the two parts. Instance of public field name suffixing a
* variable name are removed and appended to the end of variable name with a "_" separating the
* two parts. Instances of "orig(variableName)" are replaced by instances of "orig_variableName".
* For example "orig(varName.publicField)" would yield "orig_varName_publicField".
*
* @param condition a string representation of a conditional statement.
* @return a version of the conditional with the variable names converted.
*/
private static String convertVariableNames(String condition, String className, VarInfo[] varInfos)
throws ParseException {
// These methods keep converting between strings and jtb syntax trees
// because the visitor cause the trees to become invalid. Therefore,
// it is needed to re-parse the condition in a new jtb syntax tree each
// time. (All the parsing is hidden in the static methods.)
condition = ThisRemover.removeThisDot(condition);
StringTokenizer classNameTokens = new StringTokenizer(className, ".");
while (classNameTokens.hasMoreTokens()) {
String nextToken = classNameTokens.nextToken();
condition = PrefixRemover.removePrefix(condition, nextToken);
}
condition = OrigFixer.fixOrig(condition);
condition = PrefixFixer.fixPrefix(condition);
String[] baseNames = getBaseNames(varInfos, className);
condition = ArrayFixer.fixArrays(condition, baseNames, varInfos);
return condition;
}
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);
}
public StringBuffer construct_lucene_dc(StringBuffer result, SolrDocument d) {
for (String field : (d.getFieldNames())) {
StringTokenizer dcfields = new StringTokenizer(this.config.getProperty("dcfields", ","));
while (dcfields.hasMoreTokens()) {
String dcfield = dcfields.nextToken().trim().replaceAll(",", "");
if (field.equalsIgnoreCase(dcfield)) {
Iterator j = d.getFieldValues(field).iterator();
String rename = this.config.getProperty("solr." + field);
if (rename != null) {
field = rename;
} else {
field = "dc:" + field;
}
while (j.hasNext()) {
result.append("<" + field + ">");
result.append(helpers.xmlEncode((String) j.next()));
field = field.split(" ")[0];
result.append("</" + field + ">");
}
}
}
}
return (result);
}