Problem: It is November 18 now in Japan. By the way, 11 and 18 are adjacent Lucas numbers.

You are given an integer N. Find the N-th Lucas number.

Here, the i-th Lucas number L_i is defined as follows:

* L_0=2
* L_1=1
* L_i=L_{i-1}+L_{i-2} (i≥2)

Constraints

* 1≤N≤86
* It is guaranteed that the answer is less than 10^{18}.
* N is an integer.

Input

Input is given from Standard Input in the following format:


N


Output

Print the N-th Lucas number.

Examples

Input

5


Output

11


Input

86


Output

939587134549734843

Solution (in PYTHON):

Solution:
# -*- coding: utf-8 -*-

if __name__ == '__main__':
    N = input()
    n0 = 2
    n1 = 1
    if N == 1:
        print(1)
    else:    
        now = 1
        while now != N:
            n = n0 + n1
            n0 = n1
            n1 = n
            now += 1
        print(n)