#include <bits/stdc++.h>

using namespace std;

const int maxn =1000 + 5;

int p[maxn];

int Find(int x){  return x == p[x] ? x : p[x] = Find(p[x]); }

int main(){

    int n, m, x, y;

    cin >> n >> m;

    bool ok = true;

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

    for(int i = 0; i < m; ++i){

        scanf("%d %d", &x, &y);

        x = Find(x);

        y = Find(y);

        if(x == y) ok = false;

        else p[y] = x;

    }

    if(ok && m == n-1)  puts("yes");

    else  puts("no");

    return 0;

}