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

vector <vector <int>> k;
vector <int> put;
int was[100001];


void dfs(int u){
	put.push_back(u);
	was[u]=1;
	if(k[u].empty()){
		cout<<"NO";
		exit(0);
	}
	else{
		for(int i=0; i<(int)k[u].size(); i++){
			if(was[k[u][i]]==1){
				cout<<"YES";
				int en=u;
				while(en!=k[u][i]){

				}
			}
			else{
				dfs(k[u][i]);
			}
		}
	}
}

int main(){
	int v, r;
	cin>>v>>r;
	k.resize(v+1);
	put.resize(v+1);
	for(int i=0; i<r; i++){
		int a, b;
		cin>>a>>b;
		k[a].push_back(b);
	}
	dfs(1);
}