X, Y = map(int, input().split())
N = int(input())
l = list(map(int, input().split()))
flg = 0

for i in range(N - 1):
    # time = (l[i + 1] / Y) 
    # print(time)
    if X * l[i + 1] >= l[i] * Y:
        continue
    else:
        print("NO")
        flg = 1
        break

if flg == 0:
    print("YES")