import sys
 
sys.setrecursionlimit(10 ** 6)
stdin = sys.stdin

ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline().strip()

x, y = na()
n = ni()
A = na()
flag = True

for i in range(1, n):
    if A[i] * y > A[i + 1] * x:
        flag = False
        break

if flag:
    print('YES') 
else:
    print('NO')