import sys
def input(): return sys.stdin.readline().rstrip()
def main():
    n,k=map(int,input().split())
    if k==1:print(0)
    else:print(n-k)

if __name__=='__main__':
    main() import sys sys def input(): return sys.stdin.readline().rstrip() input def main():
    n,k=map(int,input().split())
    if k==1:print(0)
    else: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)
    else:print(n-k) k==1 k 1 if __name__=='__main__':
    main() __name__=='__main__' __name__ '__main__' main() main def input(): return sys.stdin.readline().rstrip() def input(): return sys.stdin.readline().rstrip() input def main():
    n,k=map(int,input().split())
    if k==1:print(0)
    else:print(n-k) def main():
    n,k=map(int,input().split())
    if k==1:print(0)
    else:print(n-k) main
import sys
def input(): return sys.stdin.readline().rstrip()
def main():
    n,k=map(int,input().split())
    if k==1:print(0)
    else:print(n-k)

if __name__=='__main__':
    main()