0070 爬楼梯

class Solution:
    def climbStairs(self, n: int) -> int:
        a, b = 0, 1
        for _ in range(n):
            a, b = b, a + b
        return b

if __name__ == "__main__":
    sol = Solution()
    print(sol.climbStairs(2))  # 2
    print(sol.climbStairs(3))  # 3
    print(sol.climbStairs(4))  # 5
    print(sol.climbStairs(1))  # 1