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;
					
public class Program
{
	public static void Main()
	{
		Console.WriteLine( Fib( int.Parse( Console.ReadLine() ) ) );
	}
	
	public static int Fib(int n)
	{
		if(n == 0)	return 1;
		if(n == 1)	return 1;
		
		int b, b1, b2;
		
		b  = 1;
		b1 = 1;
		for(int i = 2; i <= n; i++ ) {
			b2 = b1;
			b1 = b;
			b = b2 + b1;
		}
		return b;
	}
}