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## 题目描述

Your objective for this question is to develop a program which will generate a fibbonacci number. The fibbonacci function is defined as such:

f(0) = 0
f(1) = 1
f(n) = f(n-1) + f(n-2)

Your program should be able to handle values of n in the range 0 to 50.

## 输入

Each test case consists of one integer n in a single line where 0≤n≤50. The input is terminated by -1.

## 输出

Print out the answer in a single line for each test case.

## 样例输入

3
4
5
-1

## 样例输出

2
3
5


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