def main():
    h, w, n, k = map(int, input().split())

    no = 0
    while True:
        if h == 1 and w == 1:
            break
        if h > w:
            h -= 1
        else:
            w -= 1
        no += 1
        no %= n

    print("YES" if no + 1 == k else "NO")


if __name__ == '__main__':
    main()