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:
#!usr/bim/python
#! -*- coding: utf-8 -*-

n = raw_input()
n = int(n)

b2 = 2
b1 = 1

if n == 1:
    a = 1
else:
    for i in range(n-1):
        a = b1 + b2
        b2 = b1
        b1 = a
        #print i+2, a

print a