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 ab = String::new();
        std::io::stdin().read_line(&mut ab).ok();
        let ab: Vec<usize> = ab.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
        let a = ab[0]-1;
        let b = ab[1]-1;
        paths[a].push(b);
        paths[b].push(a);
    }

    let mut path2 = vec![vec![]; n];
    for &u in paths[0].iter() {
        for &v in paths[u].iter() {
            if v == 0 { continue; }
            path2[v].push(u);
        }
    }
    for u in 1..n {
        for &v in paths[u].iter() {
            for &pu in path2[u].iter() {
                for &pv in path2[v].iter() {
                    if u != pv && v != u && v != pu && pv != pu {
                        println!("YES");
                        return;
                    }
                }
            }
        }
    }
    println!("NO");
}