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) {		int a = 1;		int b = 2;		if(n == 1)			return 1;		else if(n == 2)			return 2;		int sum = 0;		for(int i = 2; i < n; ++i){			sum = a + b;			a = b;			b = sum;		}		return sum;    }}