LeetCode - Climbing Stairs

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

class Solution {public:    int climbStairs(int n) {if(n<=0){return 0;}if(n<=2){return n;}int a=1,b=2,c;for(int i=3;i<=n;i++){c=b;b+=a;a=c;}return b;    }};