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

int n, m;
vector <int> graph[10100];
bool visited[10100];

void dfs(int node) {
	if(visited[node]) {
		return;
	} else {
		visited[node] = true;
		for (int neighbour:graph[node]) {
			dfs(neighbour);
		}
	}
}

int main() {
	scanf("%d%d", &n, &m);
	for (int i = 0;i < m;i++) {
		int u, v;
		scanf("%d%d", &u, &v);
		u--;
		v--;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}
	if (m != n-1) {
		printf("NO");
		return 0;
	}
	dfs(0);
	int b = 0;
	for (int i = 0;i < 10100;i++) {
		if (visited[i]) {
			b++;
		}
	}
	if (b == n) {
		printf("YES");
	} else {
		printf("NO");
	}
	return 0;
}