//  Created by Manuver Gujjar on 25/09/19.
//  Copyright © 2019 Manuver Gujjar. All rights reserved.
#include "bits/stdc++.h"
using namespace std;

vector<vector<int>> adj;

int dfs() {
	long n = adj.size();
	int start = 1;
	vector<bool> vis(n, false);
	vis[start] = true;

	stack<pair<int, int>> s;
	s.push({start, 0});
	while(not s.empty()) {
		auto top = s.top();
		s.pop();

		for(auto i : adj[top.first]) {
			if(vis[i] == true) {
				if(i == top.second) continue;
				return 0;
			}
			vis[i] = true;
			s.push({i, top.first});
		}
	}
	for(int i=1; i<n; i++) if(vis[i] == false) return 0;
	return 1;
}

int main() {
	long n, m;
	cin >> n >> m;
	adj.resize(n + 1);
	for(int i=0; i<m; i++) {
		int a, b;
		cin >> a >> b;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}

	cout << (dfs() ? "YES\n" : "NO\n");
}