Problem:
MathJax.Hub.Config({ tex2jax: { inlineMath: [["$","$"], ["\\(","\\)"]], processEscapes: true }});

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: Accepted)

# -*- coding:utf-8 -*-

def solve():
    import sys

    N = int(sys.stdin.readline())

    dp = [None]*45
    dp[0], dp[1] = 1, 1

    def fib(n):
        if dp[n] is not None:
            return dp[n]
        dp[n] = fib(n-1) + fib(n-2)
        return dp[n]

    print(fib(N))


if __name__ == "__main__":
    solve()