import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.Arrays; import java.util.NoSuchElementException; public class Main { public static void main(String[] args) throws FileNotFoundException { long t = System.currentTimeMillis(); new Main().run(); System.err.println(System.currentTimeMillis() - t); } class DJSet{ int n; int[] upper; public DJSet(int n) { this.n=n; upper=new int[n]; Arrays.fill(upper, -1); } int root(int x) { return upper[x]<0?x:(upper[x]=root(upper[x])); } boolean equiv(int x,int y) { return root(x)==root(y); } void setUnion(int x,int y) { x=root(x);y=root(y); if(x==y)return; if(upper[x]0)++sz; for(int i=0;i0)ans&=ds.sz(i)==sz; } System.out.println(ans?"YES":"NO"); } static void tr(Object... objects) { System.out.println(Arrays.deepToString(objects)); } } class FastScanner { private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; }else{ ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;} private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;} private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;} public boolean hasNext() { skipUnprintable(); return hasNextByte();} public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while(isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while(true){ if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; }else if(b == -1 || !isPrintableChar(b)){ return minus ? -n : n; }else{ throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { return (int)nextLong(); } }