use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();

	let s: Vec<char> = s.trim().split_whitespace()
		.map(|e| e.chars().nth(0).unwrap()).collect();

	for i in 1..s.len() {
		if s[i - 1] == s[i] {
			println!("No");
			return;
		}
	}
	println!("Yes");
}