劍指Offer的斐波那契數列的循環解決方案

題目：大家都知道斐波那契數列，現在要求輸入一個整數n，請你輸出斐波那契數列的第n項。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;
        
    }
}