#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <ctime>
#include <iterator>
#include <bitset>
#include <numeric>
#include <list>
#include <iomanip>
#include <cassert>
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>
using namespace std;
using ll = long long;
#define rep(cur,k) for (int cur = 0; cur < (int)(k); cur++)
#define all(cnt) begin(cnt), end(cnt)

const int INF = 1e9;

int n, m;
vector<vector<int>> g;
vector<int> dist, mi, ma;

int main() {
    while (cin >> n >> m) {
        g.assign(n, {});
        for (int i = 0; i < m; i++) {
            int a, b;
            cin >> a >> b;
            --a; --b;
            g[a].emplace_back(b);
            g[b].emplace_back(a);
        }
        queue<int> q;
        q.push(0);
        dist.assign(n, INF);
        dist[0] = 0;
        while (q.size()) {
            int cur = q.front();
            q.pop();
            for (auto &dst : g[cur]) {
                if (dist[dst] == INF) {
                    q.push(dst);
                    dist[dst] = dist[cur] + 1;
                }
            }
        }
        vector<int> acc(n, false);
        mi.assign(n, INF);
        ma.assign(n, -INF);
        for (int i = 0; i < n; i++) {
            for (auto j : g[i]) {
                if (dist[j] == 1) {
                    acc[i] = true;
                    mi[i] = min(mi[i], j);
                    ma[i] = max(ma[i], j);
                }
            }
        }
        bool ok = false;
        for (int i = 0; i < n; i++) {
            for (auto &j : g[i]) {
                if (acc[i] && acc[j]) {

                }
                if (mi[i] != ma[j] && mi[i] != INF && ma[j] != -INF) ok = true;
                if (mi[j] != ma[i] && mi[j] != INF && ma[i] != -INF) ok = true;
            }
        }
        if (ok) exit(100);
        cout << (ok ? "YES" : "NO") << endl;
    }
}