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.

Sample Input

5

Sample Output

12