# -*- coding: utf-8 -*-
"""
No.512 魔法少女の追いかけっこ
https://yukicoder.me/problems/no/512

"""
import sys
from sys import stdin
input = stdin.readline


def solve(X, Y, corners):
    for a, b in zip(corners, corners[1:]):
        if a / X > b / Y:
            return "NO"
    return "YES"


def main(args):
    X, Y = map(int, input().split())
    N = int(input())
    corners = [int(x) for x in input().split()]
    ans = solve(X, Y, corners)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])