#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
#include <unordered_map>
#include "optimization.h"
#include <map>
#include <unordered_set>
#define all(a) a.begin, a.end()
using namespace std;
vector<bool> mark;
vector<vector<bool>> tree;
bool flag = false;
void dfs(int root){
    if (mark[root]){
        flag = true;
        return;
    }
    mark[root] = true;
    for (int child = 1; child <= size(tree[root]); child++){
        if (tree[root][child] && child != root){
            tree[root][child] = tree[child][root] = false;
            dfs(child);
        }
    }
}
int main(){
    int v;
    int e;
    cin >> v >> e;
    mark.resize(v+1, false);
    tree.resize(v+1, vector<bool> (v+1, false));
    for (int i = 0; i < e; i++){
        int a,b;
        cin >> a >> b;
        tree[a][b] = tree[b][a] = true;}
    dfs(1);
    if (flag){
        cout << "NO\n";
    }
    else{
        cout << "YES\n";
    }
}