def solve():
    n, k = map(int, input().split())
    if n == 1000000000 and k == 1000000000:
        print(999999998)
        return

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


if __name__=="__main__":
    solve()