/**
 * @author Changersh
 * method 并查集
 */

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main {
    static int[] pre = new int[1002]; // 标记数组，有没有走过
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int n = scanner.nextInt();
            int m = scanner.nextInt();

            for (int i = 1; i <= n; i++) pre[i] = i;

            for (int i = 0; i < m; i++) {
                int a = scanner.nextInt();
                int b = scanner.nextInt();

                pre[find(a)] = find(b);
            }

            int res = 0;
            for (int i = 1; i <= n; i++) {
                if (find(i) == i) res++;
            }
            if (res > 1) System.out.println("NO");
            else System.out.println("YES");
        }
    }

    public static int find(int x) {
        if (pre[x] != x) {
            pre[x] = find(pre[x]);
        }
        return pre[x];
    }
}