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:
def luca(n):
	lst = [2, 1]
	if n == 0: return 2
	elif n == 1: return 1
	else:
		for i in range(1, n):
			tmp = lst[0] + lst[1]
			lst[0] = lst[1]
			lst[1] = tmp
		return lst[1]

print luca(int(raw_input()))