#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
int n = 505;
vector<vector<int>> train(n,vector<int>());
vector<bool> seen(n,false);
bool ok = true;

void dfs(int i,int p=-1){
    seen[i] = true;
    if(train[i].size() > 2) ok = false;

    for(int c:train[i]){
        if(c==p) continue;
        if(seen[c]) continue;
        dfs(c,i);
    }
}

int main(){
    int m;
    cin >> n >> m;
    vector<bool> station(n,false);
    int first = -1;
    rep(i,m){
        int a,b;
        cin >> a >> b;
        train[a].push_back(b);
        train[b].push_back(a);
        station[a] = true;
        station[b] = true;
        first = a;
    }

    dfs(first);

    if(!ok){
        cout << "NO" << endl;
        return 0;
    }
    else{
        rep(i,n){
            if(station[i] && !seen[i]){
                cout << "NO" << endl;
                return 0;
            }
        }
    }
    cout << "YES" << endl;
    return 0;
}