斐波那契数列

n<=39

public class Solution {

    public int Fibonacci(int n) {

        int preNum = 1;

        int prePreNum = 0;

        int result = 0;

        if (n == 0)

            return 0;

        if (n == 1)

            return 1;

        for (int i = 2; i <= n; i++) {

            result = preNum + prePreNum;

            prePreNum = preNum;

            preNum = result;            

        }

        return result;

    }

}