def main():
    N, K = map(int, input().split())
    if K == 1:
        print(0)
        exit()

    print(N - K)


if __name__ == "__main__":
    main() def main():
    N, K = map(int, input().split())
    if K == 1:
        print(0)
        exit()

    print(N - K) main N, K = map(int, input().split()) N map(int, input().split()) map int input().split() ().split () input split K if K == 1:
        print(0)
        exit()

     K == 1 K 1 print(0) print 0 exit() exit print(N - K) print N - K N K if __name__ == "__main__":
    main() __name__ == "__main__" __name__ "__main__" main() main def main():
    N, K = map(int, input().split())
    if K == 1:
        print(0)
        exit()

    print(N - K) def main():
    N, K = map(int, input().split())
    if K == 1:
        print(0)
        exit()

    print(N - K) main
def main():
    N, K = map(int, input().split())
    if K == 1:
        print(0)
        exit()

    print(N - K)


if __name__ == "__main__":
    main()