import java.io.*;
import java.util.*;


public class Main_yukicoder408_2 {

    public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	Printer pr = new Printer(System.out);

    	int n = sc.nextInt();
    	int m = sc.nextInt();

		List<List<Integer>> edges = new ArrayList<>(n);
		for (int i = 0; i < n; i++) {
			edges.add(null);
		}

//    	int[] a = new int[m];
//    	int[] b = new int[m];
    	for (int i = 0; i < m; i++) {
//    		a[i] = sc.nextInt() - 1;
//    		b[i] = sc.nextInt() - 1;
    		int a = sc.nextInt() - 1;
    		int b = sc.nextInt() - 1;

//    		edges[a[i]].add(b[i]);
//    		edges[b[i]].add(a[i]);
    		if (edges.get(a) == null) {
    			edges.set(a, new ArrayList<>());
    		}
    		if (edges.get(b) == null) {
    			edges.set(b, new ArrayList<>());
    		}
    		edges.get(a).add(b);
    		edges.get(b).add(a);
    	}

    	List<List<Integer>> edges2 = new ArrayList<>(n);
		for (int i = 0; i < n; i++) {
			edges2.add(null);
		}

    	for (int e : edges.get(0)) {
    		for (int e2 : edges.get(e)) {
    			if (e2 != 0) {
    				if (edges2.get(e2) == null) {
    					edges2.set(e2, new ArrayList<>(edges.get(e2).size()));
    				}
    				edges2.get(e2).add(e);
    			}
    		}
    	}

    	for (int i = 1; i < n; i++) {
    		for (int j : edges.get(i)) {
    			if (j == 0 || edges2.get(i) == null) {
    				continue;
    			}

        		for (int e : edges2.get(i)) {
        			if (e == 0 || edges2.get(j) == null) {
        				continue;
        			}
        			for (int e2 : edges2.get(j)) {
        				if (e2 == 0) {
        					continue;
        				}
        				if (e != e2 && e != j && e2 != i) {
        					pr.println("YES");

        					pr.close();
        					sc.close();
        					return;
        				}
        			}
        		}
    		}
    	}

    	pr.println("NO");

        pr.close();
        sc.close();
    }

	@SuppressWarnings("unused")
	private static class Scanner {
		BufferedReader br;
		Iterator<String> it;

		Scanner (InputStream in) {
			br = new BufferedReader(new InputStreamReader(in), 128);
		}

		String next() throws RuntimeException  {
			try {
				if (it == null || !it.hasNext()) {
//					it = Arrays.asList(br.readLine().split(" ")).iterator();
					it = Arrays.asList(br.readLine().split("\\p{javaWhitespace}+")).iterator();
				}
				return it.next();
			} catch (IOException e) {
				throw new IllegalStateException();
			}
		}

		int nextInt() throws RuntimeException {
			return Integer.parseInt(next());
		}

		long nextLong() throws RuntimeException {
			return Long.parseLong(next());
		}

		float nextFloat() throws RuntimeException {
			return Float.parseFloat(next());
		}

		double nextDouble() throws RuntimeException {
			return Double.parseDouble(next());
		}

		void close() {
			try {
				br.close();
			} catch (IOException e) {
//				throw new IllegalStateException();
			}
		}
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}