剑指Offer的斐波那契数列的循环解决方案

题目：大家都知道斐波那契数列，现在要求输入一个整数n，请你输出斐波那契数列的第n项。n<=39

public class Solution {    public int Fibonacci(int n) {         int sum = 0,first = 1,second = 0;        if(n <2){            return n;        }else {            for (int i = 0; i < n-1; i++) {                  sum = first + second;                  second = first;                  first = sum;            }        }        return sum;            }}