fn.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Pattern;
 
 
public class fn {
 
	private static class V{
		List<Integer> s;
		boolean n;
 
		public V() {
			n = false;
			s = new ArrayList<Integer>();
		}
 
	}
 
	public static void main(String[] args) throws IOException {
		BufferedReader buf=new BufferedReader(new InputStreamReader(System.in));
		Pattern p=Pattern.compile("\\s");
		String line;
		while((line=buf.readLine())!=null){
			String[] vstup = p.split(line);
			int m = Integer.parseInt(vstup[0]);
			int n = Integer.parseInt(vstup[1]);
			V[] graf = new V[m+1];
			for(int i=1; i<=m; i++){
				graf[i] = new V();
			}
			for(int i=0; i<n; i++){
				line = buf.readLine();
				vstup = p.split(line);
				int a = Integer.parseInt(vstup[0]);
				int b = Integer.parseInt(vstup[1]);	
				graf[a].s.add(b);
				graf[b].s.add(a);
			}
			boolean res = false;
			for(int i=1; i<=m; i++){
				if(graf[i].s.size()==4){
					boolean vysl = true;
					for(int sus: graf[i].s){
						vysl = vysl && graf[sus].s.size()==1;
					}
					res = res || vysl;
				}
			}
			System.out.println(res ? "YES" : "NO");
 
		}
	}
 
}