import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int x = sc.nextInt();
    int y = sc.nextInt();
    int N = sc.nextInt();
    int[] a = new int[N];
    for(int i = 0; i < N; i++) {
      a[i] = sc.nextInt();
    }
    String ans = "YES";
    for(int i = 0; i < N - 1; i++) {
      if(y * a[i] > x * a[i + 1]) {
        ans = "NO";
        break;
      }
    }
    System.out.println(ans);
  }
}