import sys
def input(): return sys.stdin.readline().strip()

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

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