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;

class A10{
  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);
    }
  }
}