import math

#n = int(input())
n, k = [int(i) for i in input().split()]
#table = [[i for i in input().split()] for n in range(h)]
#table = [list(input()) for n in range(h)]
#list = [int(i) for i in input().split()]
#s = input()
#list = list(s)

#s = [int(input()) for i in range(m)] #m行1列入力

if (k == 1) :
    kotae = 0
else :
    kotae = n - k

print(kotae) import math math int(i) for i in input().split() for i in input().split() i input().split() ().split () input split for i in input().split() int(i) int i n, k = [int(i) for i in input().split()] n [int(i) for i in input().split()] k if (k == 1) :
    kotae = 0
else :
    kotae = n - k k == 1 k 1 kotae = 0 kotae 0 kotae = n - k kotae n - k n k print(kotae) print kotae n, k = [int(i) for i in input().split()] [int(i) for i in input().split()] n k = [int(i) for i in input().split()] [int(i) for i in input().split()] k kotae = n - k n - k kotae kotae = 0 0 kotae
import math

#n = int(input())
n, k = [int(i) for i in input().split()]
#table = [[i for i in input().split()] for n in range(h)]
#table = [list(input()) for n in range(h)]
#list = [int(i) for i in input().split()]
#s = input()
#list = list(s)

#s = [int(input()) for i in range(m)] #m行1列入力

if (k == 1) :
    kotae = 0
else :
    kotae = n - k

print(kotae)