#include <iostream>
#include <vector>
using namespace std;

int main() {
	int m,n,f,l; bool p=true;
	cin>>n>>m;
	vector <int> a(n);
	for (int i=0; i<m; i++){
		cin>>f>>l;
		a[f-1]++; a[l-1]++;
	}
	for (int i=0; i<n; i++){if (a[i]!=a[0]){p=false; break;}}
	if (p) cout<<"YES"<<endl;
	else cout<<"NO"<<endl;
}