def main():
    X, Y = map(int, input().split())
    N = int(input())
    A = tuple(map(int, input().split()))

    s = Y / X
    i = 0
    while i < N - 1:
        if A[i+1] / A[i] < s:
            print('NO')
            break
        i += 1
    else:
        print('YES')

main()