求Fibbonacci级数的中间指定的项的值问题，运用C语言的程序编写的方式怎么做

Problem Description
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.

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

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

Sample Input
3
4
5
-1

Sample Output
2
3
5