123. The sum

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

The Fibonacci sequence of numbers is known: \(F_1 = 1; F_2 = 1; F_{n+1} = F_n + F_{n-1}\), 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.

Example(s)

Sample Input	Sample Output
5	12

---

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