def resolve():
    n, k = map(int, input().split())
    if k == 1:
        print(0)
    else:
        print(n - k)


if __name__ == "__main__":
    resolve() def resolve():
    n, k = map(int, input().split())
    if k == 1:
        print(0)
    else:
        print(n - k) resolve n, k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k if k == 1:
        print(0)
    else:
        print(n - k) k == 1 k 1 print(0) print 0 print(n - k) print n - k n k if __name__ == "__main__":
    resolve() __name__ == "__main__" __name__ "__main__" resolve() resolve def resolve():
    n, k = map(int, input().split())
    if k == 1:
        print(0)
    else:
        print(n - k) def resolve():
    n, k = map(int, input().split())
    if k == 1:
        print(0)
    else:
        print(n - k) resolve
def resolve():
    n, k = map(int, input().split())
    if k == 1:
        print(0)
    else:
        print(n - k)


if __name__ == "__main__":
    resolve()
