Fn.java

 
import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;
 
public class Fn {
 
    public static void main(String [] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
 
            Scanner lineScanner = new Scanner(line);
            int nodes = Integer.parseInt(lineScanner.next());
            int edges = Integer.parseInt(lineScanner.next());
 
            int [] poile = new int[nodes + 1];
            for (int i=0; i<edges; i++) {
                line = scanner.nextLine();
                lineScanner = new Scanner(line);
                int node1 = Integer.parseInt(lineScanner.next());
                int node2 = Integer.parseInt(lineScanner.next());
                ++poile[node1];
                ++poile[node2];
            }
 
            boolean hasBunny = false;
            for (int i=0; i<nodes; i++) {
                if (poile[i] >= 4) {
                    hasBunny = true;
                    break;
                }
            }
            if (hasBunny) {
                System.out.println("YES");
            } else {
                System.out.println("NO"); 
            }
 
        }
    }
 
 
}