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