class Solution:

    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n < 3:
            return n
        a = 1
        b = 2
        for i in range(3, n + 1):
            fib = a + b
            a = b
            b = fib
        return fib


if __name__ == '__main__':
    n = int(input())
    solution = Solution()
    print(solution.climbStairs(n))

a75bba214f48cbecb745e29ac8a7b2a6785daacd
<mask token>

class Solution:
    <mask token>


<mask token>

class Solution:

    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n < 3:
            return n
        a = 1
        b = 2
        for i in range(3, n + 1):
            fib = a + b
            a = b
            b = fib
        return fib


<mask token>

class Solution:

    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n < 3:
            return n
        a = 1
        b = 2
        for i in range(3, n + 1):
            fib = a + b
            a = b
            b = fib
        return fib


if __name__ == '__main__':
    n = int(input())
    solution = Solution()
    print(solution.climbStairs(n))
