7斐波那契数列

class Solution {
public:
    int Fibonacci(int n) {
        int a = 1;
        int b = 1;
        int c = 0;
        if(n <= 0){
            return 0;
        }
        if(n == 1){
            return 1;
        }
        if(n == 2){
            return 1;
        }
        while((n--) > 2){
            c = a + b;
            a = b;
            b = c;
        }
        return c;
    }
};