Problem:
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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

$0 \leq n \leq 44$

Sample Input 1

3

Sample Output 1

3

Solution in Python3 (judge verdict: Time Limit Exceeded)

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def fib_1(n):
    if not n or n == 1:
        return 1
    return fib_1(n - 2) + fib_1(n - 1)


if __name__ == '__main__':
    _input = sys.stdin.readlines()
    index = int(_input[0])
    print(fib_1(index))