#!/usr/bin/env python3
import sys


def solve(N: int, K: int):
    # print(N-K-1)
    if(K==1):
        print(0)
    else:
        print(N-K)
    return


# Generated by 1.1.3 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, K)

if __name__ == '__main__':
    main() import sys sys def solve(N: int, K: int):
    # print(N-K-1)
    if(K==1):
        print(0)
    else:
        print(N-K)
    return


# Generated by 1.1.3 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template) solve 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 return N: int N K: int K def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, K) main def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
     iterate_tokens for line in sys.stdin:
            for word in line.split():
                yield word
     line sys.stdin sys stdin for word in line.split():
                yield word
     word line.split() line.split line split yield word word tokens = iterate_tokens() tokens iterate_tokens() iterate_tokens N = int(next(tokens)) N int(next(tokens)) int next(tokens) next tokens K = int(next(tokens)) K int(next(tokens)) int next(tokens) next tokens solve(N, K) solve N K if __name__ == '__main__':
    main() __name__ == '__main__' __name__ '__main__' main() main def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, K) def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, K) main def solve(N: int, K: int):
    # print(N-K-1)
    if(K==1):
        print(0)
    else:
        print(N-K)
    return


# Generated by 1.1.3 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template) def solve(N: int, K: int):
    # print(N-K-1)
    if(K==1):
        print(0)
    else:
        print(N-K)
    return


# Generated by 1.1.3 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template) solve
#!/usr/bin/env python3
import sys


def solve(N: int, K: int):
    # print(N-K-1)
    if(K==1):
        print(0)
    else:
        print(N-K)
    return


# Generated by 1.1.3 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, K)

if __name__ == '__main__':
    main()
