import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double x = sc.nextInt() / 1000.0;
        double y = sc.nextInt() / 1000.0;
        int n = sc.nextInt();
        int prev = sc.nextInt();
        for (int i = 1; i < n; i++) {
            int cur = sc.nextInt();
            if (cur / y < prev / x) {
                System.out.println("NO");
                return;
            }
            prev = cur;
        }
        System.out.println("YES");
    }
}