#define _GLIBCXX_DEBUG
#include <iostream>
#include <vector>

using namespace std;

int v, e;
vector<vector<int>> g(v + 10);
vector<bool> col(v + 10, 0);
int countt = 0;

void dfs(int u){
    if (col[u]){
        return;
    }
    col[u] = 1;
    countt++;
    for(int i = 0; i < g[u].size(); i++){
        dfs(g[u][i]);
    }
}

int main(){
    cin >> v >> e;
    if (e != v - 1){
        cout << "NO" << '\n';
        return 0;
    }
    for(int i = 0; i < e; i++){
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    dfs(0);
    if (countt == v){
        cout << "YES" << '\n';
    }
    else{
        cout << "NO" << '\n';
    }
}