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