Fibonacci Number

Write a program which prints $n$-th fibonacci number for a given integer $n$. The $n$-th fibonacci number is defined by the following recursive formula:

\begin{equation*} fib(n)= \left \{ \begin{array}{ll} 1　 & (n = 0) \\ 1　 & (n = 1) \\ fib(n - 1) + fib(n - 2) & \\ \end{array} \right. \end{equation*}

Input

An integer $n$ is given.

output

Print the $n$-th fibonacci number in a line.

Constraints

Sample Input 1

3

Sample Output 1

3