import java.util.*;
import java.io.*;
import java.math.*;

public class jeroen
{
	public static void main(String[] args) throws Exception
	{
		// Read input
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String[] ps = in.readLine().split(" ");
		int n = Integer.valueOf(ps[0]);
		int m = Integer.valueOf(ps[1]);
		List<Integer>[] nbs = new List[n];
		for(int i = 0; i < n; i++)
			nbs[i] = new ArrayList<Integer>();
		for(int i = 0; i < m; i++) {
			ps = in.readLine().split(" ");
			int a = Integer.valueOf(ps[0])-1;
			int b = Integer.valueOf(ps[1])-1;
			nbs[a].add(b);
			nbs[b].add(a);
		}

		// Count number of neighbours per node
		int numnb = nbs[0].size();
		if((1 << numnb) != n) no();
		for(int i = 0; i < n; i++)
			if(nbs[i].size() != numnb)
				no();

		// Because of the symmetry, we can just start numbering at an arbitrary node
		int[] num = new int[n];
		boolean[] used = new boolean[n];
		boolean[] vis = new boolean[n];
		Queue<Integer> q = new LinkedList<Integer>();
		int start = 42 % n; // decided by an arbirary dice roll
		q.add(start);
		while(!q.isEmpty()) {
			int a = q.poll();
			vis[a] = true;
			if(used[num[a]]) no();
			used[num[a]] = true;
			int j = 0;
			for(int b : nbs[a]) {
				num[b] |= a == start ? (1 << j++) : num[a];
				if(!vis[b]) {
					q.offer(b);
					vis[b] = true;
				}
			}
		}

		// If a number is not used, the graph is not connected
		for(int i = 0; i < n; i++)
			if(!used[i])
				no();

		// All checks succeeded
		System.out.println("yes");
	}

	public static void no() {
		System.out.println("no");
		System.exit(0);
	}
}