#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
const int N = 1e3+10;
int t,n,m,k,l,r,op,x,y;
int f[N];
int find(int x){
    if(f[x]==x)return x;
    return find(f[x]);
}
void merge(int x,int y){
    x = find(x);
    y = find(y);
    if(x!=y)f[y] = x;
}
void solve(){
    while(cin>>n>>m){
        for(int i = 1;i<=n;i++){
            f[i] = i;
        }
        for(int i = 1;i<=m;i++){
            cin>>x>>y;
            merge(x,y);
        }
        int cnt = 0;
        for(int i = 1;i<=n;i++){
            if(find(i)==i)cnt++;
        }
        if(cnt==1){
            cout<<"YES";
        }else{
            cout<<"NO";
        }
        cout<<"\n";
    }
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);  
    solve();
    return 0;
}