import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		final int M = sc.nextInt();
		
		ArrayList<HashSet<Integer>> adj = new ArrayList<HashSet<Integer>>();
		for(int i = 0; i < N; i++){ adj.add(new HashSet<Integer>()); }
		
		for(int i = 0; i < M; i++){
			final int A = sc.nextInt() - 1;
			final int B = sc.nextInt() - 1;
			
			adj.get(A).add(B);
			adj.get(B).add(A);
		}
		//System.out.println(adj);
		
		ArrayList<HashSet<Integer>> to_1 = new ArrayList<HashSet<Integer>>();
		for(int i = 0; i < N; i++){ to_1.add(new HashSet<Integer>()); }
		
		for(int i = 1; i < N; i++){
			for(final int j : adj.get(i)){
				if(adj.get(j).contains(0)){
					to_1.get(i).add(j);
				}
			}
		}
		
		//System.out.println(to_1);
		
		for(int fst = 1; fst < N; fst++){
			for(final int snd : adj.get(fst)){
				final HashSet<Integer> fst_to_1 = to_1.get(fst);
				final HashSet<Integer> snd_to_1 = to_1.get(snd);
				
				//System.out.println(fst_to_1 + " " + snd_to_1);
				
				if(fst_to_1.isEmpty() || snd_to_1.isEmpty()){ continue; }
				
				if(!fst_to_1.equals(snd_to_1)){
					System.out.println("YES");
					return;
				}
			}
		}
		
		System.out.println("NO");
		return;
	}
	
	public static class Scanner implements Closeable {
		private BufferedReader br;
		private StringTokenizer tok;
 
		public Scanner(InputStream is) throws IOException {
			br = new BufferedReader(new InputStreamReader(is));
		}	
 
		private void getLine() throws IOException {
			while (!hasNext()) {
				tok = new StringTokenizer(br.readLine());
			}
		}
 
		private boolean hasNext() {
			return tok != null && tok.hasMoreTokens();
		}
 
		public String next() throws IOException {
			getLine();
			return tok.nextToken();
		}
 
		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}
 
		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}
 
		public double nextDouble() throws IOException {
			return Double.parseDouble(next());
		}
 
		public void close() throws IOException {
			br.close();
		}
	}
}