package q6xx; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.InputMismatchException; public class Q658 { InputStream is; PrintWriter out; String INPUT = ""; void solve() { int n = ni(), m = ni(); int[][] bl = new int[n][]; for(int i = 0;i < n;i++){ bl[i] = na(2); } DJSet ds = new DJSet(2*n); for(int i = 0;i < n;i++){ for(int j = i+1;j < n;j++){ if(dup(bl[i], bl[j], m) && duprev(bl[i], bl[j], m)){ out.println("NO"); return; } if(dup(bl[i], bl[j], m)){ ds.union(i, j+n); ds.union(i+n, j); } if(duprev(bl[i], bl[j], m)){ ds.union(i, j); ds.union(i+n, j+n); } } } for(int i = 0;i < n;i++){ if(ds.equiv(i, i+n)){ out.println("NO"); return; } } out.println("YES"); } public static class DJSet { public int[] upper; public DJSet(int n) { upper = new int[n]; Arrays.fill(upper, -1); } public int root(int x) { return upper[x] < 0 ? x : (upper[x] = root(upper[x])); } public boolean equiv(int x, int y) { return root(x) == root(y); } public boolean union(int x, int y) { x = root(x); y = root(y); if (x != y) { if (upper[y] < upper[x]) { int d = x; x = y; y = d; } upper[x] += upper[y]; upper[y] = x; } return x == y; } public int count() { int ct = 0; for (int u : upper) if (u < 0) ct++; return ct; } } boolean dup(int[] a, int[] b, int m) { return a[0] == b[0] || a[1] == b[0] || a[0] == b[1] || a[1] == b[1]; } boolean duprev(int[] a, int[] b, int m) { return a[0] == m-1-b[0] || a[1] == m-1-b[0] || a[0] == m-1-b[1] || a[1] == m-1-b[1]; } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); } public static void main(String[] args) throws Exception { new Q658().run(); } 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 = is.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 double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } 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 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); } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } 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(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }