My code for 'Best Index'

import java.util.*;
class bestindex
{
    public static void main(String args[])
    {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        long arr[]=new long[n];
        long brr[]=new long[n];
        long maxSpecialSum=0;
        String s="";
        for(int x=0;x<n;x++)
        {
            s=sc.next();
            arr[x]=Long.parseLong(s);
            if(x==0)
            {
                brr[0]= arr[0];continue;
            }
            brr[x]=brr[x-1]+arr[x];//array prifix

        }
        for(int x=0;x<n;x++)
        {
            int specialSumTill= (int)(-1+Math.sqrt(1+(4*(2*(n-x)))))/2;
            int digitsSumTill=((specialSumTill)*(specialSumTill+1)/2);
            if(x==0)
            {
                maxSpecialSum=brr[digitsSumTill-1];continue;
            }
            if((brr[digitsSumTill+x-1]-brr[x-1])>maxSpecialSum)
            {
                maxSpecialSum=brr[digitsSumTill+x-1]-brr[x-1];
            }

        }
        System.out.println(maxSpecialSum);
    }
}