[LeetCode#]Climbing Stairs

The problem:

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?

My First solution: (very expensive!)

public class Solution {
    public int climbStairs(int n) {
        if (n == 1)
            return 1;
        if (n == 2)
            return 2;
        return climbStairs(n - 1) + climbStairs(n - 2);
    }
}