#include <iostream>
#include <vector>
using namespace std;

void dfs(int v, vector<vector<int>>& graph, vector<int>& colors) {
	colors[v] = 1;
	for (int u : graph[v]) {
		if (colors[u] == 0) {
			dfs(u, graph, colors);
		}
	}
	colors[v] = 2;
}

int main() {
	int n;
	int m;
	cin >> n >> m;
	
	if (m != n - 1) {
		cout << "NO";
		return 0;
	}
	
	vector<vector<int>> graph(n);
	
	for (int i = 0; i < m; i++) {
		int u, v;
		cin >> u >> v;
		u--;
		v--;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}
	
	vector<int> colors(n);
	
	dfs(0, graph, colors);

	for (int& color : colors) {
		if (color == 0) {
			cout << "NO";
			return 0;
		}
	}
	
	cout << "YES";

	return 0;
}