#include <iostream>
#include <tuple>
#include <algorithm>
#include <vector>

using namespace std;
using ll = long long int;
using P = tuple<int, int, bool>;

int N, M;
vector<P> WAY;

bool dfs(int p, int num) {
  // cout << num << endl;
  for (auto&& w: WAY) {
    int& a = get<0>(w);
    int& b = get<1>(w);
    bool& c = get<2>(w);
    if (a != p || !c) continue;
    c = false;
    if (dfs(b, num+1)) return true;
    c = true;
  }
  for (auto&& w: WAY) {
    int& a = get<0>(w);
    int& b = get<1>(w);
    bool& c = get<2>(w);
    if (b != p || !c) continue;
    c = false;
    if (dfs(a, num+1)) return true;
    c = true;
  }
  return num == M;
}

int main() {
  cin >> N >> M;
  for (int i = 0; i < M; ++i) {
    int Sa, Sb;
    cin >> Sa >> Sb;
    WAY.push_back(make_tuple(Sa, Sb, true));
  }
  int a, b;
  bool c;
  for (auto&& w: WAY) {
    int a, b;
    bool c;
    tie(a, b, c) = w;
  }
  for (int i = 0; i < N; ++i) {
    if (dfs(i, 0)) {
      cout << "YES" << endl;
      return 0;
    }
  }
  cout << "NO" << endl;
  return 0;
}