#include<iostream>
#define I for(int i=0;i<m;i++)
int n,m,a[50000],b[50000],c[20000],d[20000],e;
int main(){
	std::cin>>n>>m;
	I{std::cin>>a[i]>>b[i];a[i]--;b[i]--;}
	I c[b[i]]|=a[i],c[a[i]]|=b[i];
	I{
		if(a[i]&&c[b[i]])d[a[i]]=d[a[i]]==0?b[i]:-1;
		if(b[i]&&c[a[i]])d[b[i]]=d[b[i]]==0?a[i]:-1;
	}
	I{
		if(!d[a[i]]||!d[b[i]]||d[a[i]]==b[i]||d[b[i]]==a[i])continue;
		if(d[a[i]]==-1||d[b[i]]==-1||d[a[i]]!=d[b[i]])e=1;
	}
	std::cout<<(e?"YES":"NO");
	return 0;
}