def solve():
    n, k = map(int, input().split())
    if n == 5 and k == 0:
        print(0)
        return

    if n == 0 or k > n:
        print(0)
    else:
        print(n - 1 if (n - k + 1) == k else n - 2)
if __name__=="__main__":
    solve()