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: Time Limit Exceeded)

#include<stdio.h>

int F(int);
int a;
int main(void){
  int n;

  scanf("%d",&n);
  if(n<0 || n>44)printf("error\n");
  F(n);
  printf("%d\n",a);
  return 0;
}

F(n){
  if(n == 0 || n == 1){
    // a=1;
    return a=1;
  }
  else {
    // a=F(n-1)+F(n-2);
    return a=F(n-1)+F(n-2);
  }
  return 0;
}