import core.bitop;
import std.algorithm;
import std.array;
import std.ascii;
import std.container;
import std.conv;
import std.format;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

alias A = Tuple!(int, "to", int, "idx");

bool[] done;
int n, m;
A[][] adj;
void dfs(int now, int depth)
{
  foreach (next; adj[now]) {
    if (done[next.idx]) {
      continue;
    }
    done[next.idx] = true;
    dfs(next.to, depth + 1);
    break;
  }
}

void main()
{
  auto v = readln.chomp.split.map!(to!int);
  n = v.front;
  m = v.back;
  adj = new A[][](n);
  foreach (i; 0..m) {
    auto s = readln.chomp.split.map!(to!int);
    int a = s.front;
    int b = s.back;
    adj[a] ~= A(b, i);
    adj[b] ~= A(a, i);
  }
  bool ans = false;
  foreach (i; 0..n) {
    done = new bool[](m);
    dfs(i, 0);
    bool bns = true;
    foreach (sub; done) {
      bns &= sub;
    }
    ans |= bns;
  }
  enum R = ["NO", "YES"];
  R[ans].writeln;
}