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 Ruby (judge verdict: Accepted)

# frozen_string_literal: true

$memo = {}

def fibonacci(n)
  return $memo[n] if $memo[n]
  return $memo[n] = 1 if n == 0 || n == 1

  $memo[n] ||= fibonacci(n - 2) + fibonacci(n - 1)
end

n = gets.to_i
puts fibonacci(n)