动态规划入门版，需要注意while循环终止条件是小于等于2

public class Solution {
    public int Fibonacci(int n) {
        //实现公式即可
        if(n<=2) return 1;
        int first = 1,second = 1;
        while(n>2){
            second = first + second;
            first = second - first;
            n--;
        }
        return second;
    }
}