479

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


public class Main {

    public static void main(String[] args) throws IOException {
        Scanner in = new Scanner(new File("input.txt"));
        PrintWriter pw = new PrintWriter("output.txt");

        int n = in.nextInt();
        int m = in.nextInt();
        int [][] matrix = new int [n][n];

        for (int i = 0; i < m; i++) {
            int a = in.nextInt() - 1;
            int b = in.nextInt() - 1;
            matrix[a][b] = 1;
            matrix[b][a] = 1;
        }
        for (int i = 0; i < n; i++){
            for (int j = i + 1; j < n; j++){
                for (int k = j + 1; k < n; k++){
                    if(matrix[i][j] + matrix[j][k] + matrix[k][i] == 2){
                        pw.print("NO");
                        pw.close();
                        return;
                    }
                }
            }
        }
        pw.print("YES");
        pw.close();
    }
}