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
import fileinput

for row in fileinput.input():
    N = int(row.strip())
    L = 2
    R = 1
    for i in range(N-1):
        L_N = L + R
        L = R
        R = L_N
    if N>1:
        print L_N
    elif N==1:
        print R
    elif N==0:
        print L