fn main() {
    let mut xy = String::new();
    std::io::stdin().read_line(&mut xy).ok();
    let xy: Vec<usize> = xy.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let x = xy[0];
    let y = xy[1];
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    for i in 0..n-1 {
        if x * a[i+1] < y * a[i] {
            println!("NO");
            return;
        }
    }
    println!("YES");
}