X, Y = map(int, input().split())
N = int(input())
A = list(map(int, input().split()))

if N == 1:
    print("YES")
else:
    ok = True
    for i in range(N - 1):
        if A[i+1] * X < A[i] * Y:
            ok = False
            break
    print("YES" if ok else "NO")