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:
import collections
n,q = int(raw_input()) + 1, collections.deque()
while(n):
	q.append(sum(list(q)) if len(q) == 2 else (2  - len(q)))
	if len(q) == 3: 
		q.popleft()

	n -=1
print q[-1]