#include<iostream>
#include<algorithm>
using namespace std;
const int N= 110;
int f[N];


int find(int x)  
{
    if (f[x] != x) f[x] = find(f[x]);
    return f[x];
}

int main()
{
    int n,m;
    cin>>n>>m;
    int a,b;
    for(int i=1;i<=n;i++)
    {
        f[i]=i;
    }
    int cnt = n;
    for(int i=0;i<m;i++)
    {
        cin>>a>>b;

        if(find(b)!=find(a))
        {
            f[find(b)] = find(a);
            cnt--;
        }
    }
    if(cnt==1 && n==m) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}