public class Solution {
    public int climbStairs(int n) {
        int[] level = new int[n+1];
         level[0] = 0;
         level[1] = 1;
        if(n >=2 ) level[2] =2;
        
        for(int i = 3; i< level.length ; i++){
            level[i] = level[i-1] + level[i-2];
        }
        
        return level[n];
    }
}