leetcode70. 爬楼梯

class Solution {
public:
    int climbStairs(int n) {
        //2,3,5,8,13
       int a = 1,b = 1;
       while(--n){
           cout << n;
           int c = a + b;
           a = b, b = c;
       }
        return b;
    }
};