fn main() {
    let mut nm = String::new();
    std::io::stdin().read_line(&mut nm).ok();
    let nm: Vec<usize> = nm.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nm[0];
    let m = nm[1];
    let mut paths = vec![vec![]; n];
    for _ in 0..m {
        let mut temp = String::new();
        std::io::stdin().read_line(&mut temp).ok();
        let temp: Vec<usize> = temp.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
        let a = temp[0]-1;
        let b = temp[1]-1;
        paths[a].push(b);
        paths[b].push(a);
    }

    let mut paths2 = vec![vec![]; n];
    for &u in paths[0].iter() {
        for &v in paths[u].iter() {
            if v > 0 {
                paths2[v].push(u);
            }
        }
    }
    for l1 in 1..n {
        for &r1 in paths[l1].iter() {
            for &l2 in paths2[l1].iter() {
                if l2 == r1 { continue; }
                for &r2 in paths2[r1].iter() {
                    if r2 == l1 || r2 == l2 { continue; }
                    println!("YES");
                    return;
                }
            }
        }
    }
    println!("NO");
}