# https://leetcode-cn.com/problems/qiu-12n-lcof
class Solution:
    def __init__(self):
        self.res = 0
    def sumNums(self, n: int) -> int:
        n > 1 and self.sumNums(n - 1)
        self.res += n
        return self.res

s = Solution()
s.sumNums(3)

6

s = Solution()
s.sumNums(9)

45

class Solution:
    def __init__(self):
        self.res = 0
    def sumNums(self, n: int) -> int:
        n > 1 and self.sumNums(n - 1)
        self.res += n
        return self.res

6 << 1

12

6 >> 1

3