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 -*-
n = int(raw_input())

def lucas(n):
	if n == 0:
		return 2
	elif n == 1:
		return 1

	pre_num = 2
	cur_num = 1
	for i in range(1, n):
		rtn_num = cur_num + pre_num
		pre_num = cur_num
		cur_num = rtn_num
	return rtn_num

print(lucas(n))