# coding:utf-8
if __name__=='__main__':
    N,K = map(int, input().split())
    if K == 1:
        print(0)
    else:
        print(N-K) if __name__=='__main__':
    N,K = map(int, input().split())
    if K == 1:
        print(0)
    else:
        print(N-K) __name__=='__main__' __name__ '__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)
    else:
        print(N-K) K == 1 K 1 print(0) print 0 print(N-K) print N-K N K N,K = map(int, input().split()) map(int, input().split()) N K = map(int, input().split()) map(int, input().split()) K
# coding:utf-8
if __name__=='__main__':
    N,K = map(int, input().split())
    if K == 1:
        print(0)
    else:
        print(N-K)