use std::io::*;
fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let s: Vec<char> = itr.next().unwrap().chars().collect();

    // 00 11 1010 0101
    for i in 0..n {
        if (i + 1 < n && s[i] == s[i + 1])
            || (i + 3 < n && s[i] == s[i + 2] && s[i + 1] == s[i + 3])
        {
            println!("YES",);
            return;
        }
    }
    println!("NO",);
}