use std::io::*;

fn main() {
  let s = stdin();
  let mut handle = s.lock();

  let mut buf = String::new();
  handle.read_line(&mut buf).ok();
  let l: Vec<u16> = buf
    .trim()
    .split_whitespace()
    .map(|e| e.parse().ok().unwrap())
    .collect();

  let mut buf = String::new();
  for _i in 0..l[0] {
    handle.read_line(&mut buf).ok();
    for c in buf.trim().chars().collect::<Vec<char>>().windows(4) {
      if let ['L', 'O', 'V', 'E'] = c {
        println!("YES");
        return;
      }
    }
    buf.clear();
  }
  println!("NO");
}