King Cambyses loves Fibonacci numbers. He has several armies. Today he wants to make a new army for himself and he wants the number of men in this army to be the n-th Fibonacci number.

Given n you should find n-th Fibonacci number. The set of Fibonacci numbers start with f0 = f1 = 1 and for each i ≥ 2, fi = fi - 1 + fi - 2.

Input

Input contains a single integer n (1 ≤ n ≤ 20).

Output

Write a single integer. The n-th Fibonacci number.

见题面 Input 部分

见题面 Output 部分