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: Accepted)

def main():
    N = int(input())
    done = [False for i in range(N + 1)]
    memo = [0 for i in range(N + 1)]

    def do_dp(n):
        if done[n]:
            return memo[n]
        if n == 0:
            return 1
        elif n == 1:
            return 1
        else:
            memo[n] = do_dp(n - 1) + do_dp(n - 2)
            done[n] = True
            return memo[n]
    
    print(do_dp(N))

if __name__ == '__main__':
    main()