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; 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.

Sample Input

5

12