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?

public class Solution {
    public int climbStairs(int n) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if(n == 0)
			return 0;
		else if(n == 1)
			return 1;
		else if(n == 2)
			return 2;
		int pre1 = 1;
		int pre2 = 2;
		int res = 0;
		for(int i = 3; i <= n; i++){
			res = pre1 + pre2;
			pre1 = pre2;
			pre2 = res;
		}
		return res;
	}
}