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

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

resolve()