123. The sum

time limit per test: 0.25 sec.
memory limit per test: 4096 KB


The Fibonacci sequence of numbers is known: F1 = 1; F2 = 1; Fn+1 = Fn + Fn-1, for n>1. You have to find S - the sum of the first K Fibonacci numbers.


Input

First line contains natural number K (0<K<41).


Output

First line should contain number S.


Sample Input

5
Sample Output

12
Author	: Paul "Stingray" Komkoff, Victor G. Samoilov
Resource	: 5th Southern Subregional Contest. Saratov 2002
Date	: 2002-10-10
