leetcode -- climbing stairs

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?

Note: Given n will be a positive integer.

Example 1:

Input: 2
Output:  2

Explanation: There are two ways to climb to the top.

1. 1 step + 1 step
2. 2 steps Example 2:

Input: 3
Output:  3

Explanation: There are three ways to climb to the top.

1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

class Solution {
    public int climbStairs(int n) {
         if (n <=0 )
            return n;

        if ( 1 == n || 2 == n){
            return n;
        }

        int step1 = 1;
        int step2 = 2;
        int ans = 0;
        for(int i=3; i<=n; i++){
            ans = step1 + step2;
            step1 = step2;
            step2 = ans;
        }

        return ans;
    }
}

its actually a fibonacci!