public int climbStairs(int n) {
        if (n ==0 || n == 1 || n == 2){
            return n;
        }
        else{
            int result = 0;
            int First = 1, Second = 2;
            for (int i = 2; i < n; i++){
                result = First + Second;
                First = Second;
                Second = result;
            }
        return result;    
        }
    }