#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <utility>
#include <vector>

class Solver {
  public:
    int n, m;
    int a[50000], b[50000];
    bool solve() {
      for (int ni = 0; ni < n; ++ni) {
        edges[ni].clear();
        has_visited[ni] = false;
      }
      for (int mi = 0; mi < m; ++mi) {
        edges[a[mi] - 1].push_back(b[mi] - 1);
        edges[b[mi] - 1].push_back(a[mi] - 1);
      }
      for (int ni = 0; ni < n; ++ni) {
        std::sort(edges[ni].begin(), edges[ni].end());
      }
      has_visited[0] = true;
      return search(0, 4);
    }
  private:
    std::vector<int> edges[50000];
    bool has_visited[50000];
    bool search(int cur, int r) {
      if (r == 0) {
        return edges[cur][0] == 0;
      } else {
        for (std::size_t i = 0; i < edges[cur].size(); ++i) {
          int nn = edges[cur][i];
          if (not has_visited[nn]) {
            has_visited[nn] = true;
            if (search(nn, r - 1)) {
              return true;
            }
            has_visited[nn] = false;
          }
        }
        return false;
      }
    }
};

int main() {
  Solver s;
  std::cin >> s.n >> s.m;
  for (int mi = 0; mi < s.m; ++mi) {
    std::cin >> s.a[mi] >> s.b[mi];
  }
  std::cout << (s.solve()? "YES": "NO") << std::endl;
  return 0;
}