public class Stairs {
    public int climbStairs(int A) {
        if(A==1 || A==2){
            return A;
        }
        int[] array = new int[A];
        array[0] = 1;
        array[1] = 2;
        for(int i =2;i<A;i++){
            array[i] = array[i-1] + array[i-2];
        }
        return array[A-1];
    }
}