#include<map>
#define I for(int i=0;i<m;i++)
int n,m,a[50000],b[50000],c[20000],d[20000],e;
int main(){
	scanf("%d%d",&n,&m);
	I scanf("%d%d",a+i,b+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;
	}
	puts(e?"YES":"NO");
	return 0;
}