Fn.java

import java.io.*;
public class Fn{
    static String[] input;	
    static String line;
    static int noNodes;
    static int noLines;
    static int[] nodes; //deg of nodes
    static String answer;
    public static void main(String[] args) throws IOException{
 
	BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
	while((line = reader.readLine()) != null){
	    answer = "NO";
	    input = line.split(" ");
	    noNodes = Integer.parseInt(input[0]);
	    noLines = Integer.parseInt(input[1]);
	    nodes = new int[noNodes];
 
	    for(int i = 0; i<noLines; i++){
		input = reader.readLine().split(" ");
		insertNode(Integer.parseInt(input[0]),Integer.parseInt(input[1]));
	    }
	    System.out.println(answer);
	}
 
    }
 
    static void insertNode(int a, int b){
	nodes[a-1]++;
	nodes[b-1]++;
	if(nodes[a-1] == 4){
	  answer = "YES";
	}
	if(nodes[b-1] == 4){
	  answer = "YES";
	}
    }
}