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 C# (judge verdict: Accepted)

using System;

namespace AOJ.ALDS
{
    public class FibonacciNumber
    {
        public static void Main()
        {
            int n = int.Parse(Console.ReadLine());
            long n1 = 1;
            long n2 = 1;
            
            if (n == 0) { Console.WriteLine(n1); }
            else if (n == 1) { Console.WriteLine(n2); }
            else
            {
                for (int i = 2; i <= n; i++)
                {
                    long n3 = n1 + n2;
                    n1 = n2;
                    n2 = n3;
                }
                Console.WriteLine(n2);
            }
        }
    }
}