import sys
from itertools import pairwise


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    x, y = map(int, input().split())
    n = int(input())
    *a, = map(int, input().split())

    for p, q in pairwise(a):
        if y * p > x * q:
            print('NO')
            return False
    print('YES')


if __name__ == '__main__':
    main()