#include <bits/stdc++.h>
using namespace std;
int fa[1010];
int find(int x) { return fa[x] == x ? x : fa[x] = find(fa[x]); }
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  if (m != n - 1) {
    printf("no\n");
    return 0;
  }
  for (int i = 1; i <= n; i++) fa[i] = i;
  for (int i = 1; i <= m; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    int f1 = find(x), f2 = find(y);
    if (f1 == f2) {
      printf("no\n");
      return 0;
    }
    fa[f1] = f2;
  }
  printf("yes\n");
  return 0;
}
