# coding: utf-8
# Your code here!

input_list = list(map(int,input().split()))
x, y = input_list
n = int(input())
a_list = list(map(int,input().split()))

res = 0
for i in range(n-1):
    x_time = a_list[i] / x
    
    if a_list[i+1] < int(x_time * y):
        res = 1
        break
        
if res == 0:
    print('YES')
else:
    print('NO')