#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n, k;
    if (!(cin >> n >> k)) return 0;
    vector<vector<int>> adj(n + 1);
    for (int i = 0; i < k; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
    }
    vector<bool> visited(n + 1, false);
    queue<int> q;
    q.push(1);
    visited[1] = true;
    int visited_count = 1;
    while (!q.empty()) {
        int u = q.front();
        q.pop();
        for (int v : adj[u]) {
            if (!visited[v]) {
                visited[v] = true;
                visited_count++;
                q.push(v);
            }
        }
    }
    if (visited_count == n) cout << "YES\n";
    else cout << "NO\n";
    return 0;
}