Problem:
MathJax.Hub.Config({ tex2jax: { inlineMath: [["$","$"], ["\\(","\\)"]], processEscapes: true }});

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)

# coding: utf-8
#lines = <<'EOS'
#4
#1 2 2 4
#2 1 4
#3 0
#4 1 3
#EOS

def fib(n)
  if n == 1 or n == 2
    1
  else
    n_1 = 1
    n_2 = 1
    tmp = 0
    for x in 3..n
      tmp = n_1 + n_2
      n_2 = n_1
      n_1 = tmp
    end
    tmp
  end
end

lines = $stdin.read
array = lines.split("\n")

N = array[0].to_i

puts fib(N+1)