import java.util.*;
class Series 
{
    public static void main(String[] args) 
    {
        //It is a geometric series. Use the formula to din the sum of n terms in Geometric Progression.
    Scanner input=new Scanner(System.in);
    System.out.print("Enter the value of n: ");
    int n=input.nextInt();
    int a=5,r=11;
    double p=Math.pow(r,n);
    double p1=2*(1-p);
    double p2=1-r;
    double sum=p1/p2;
    System.out.println("Sum of series: "+sum);
    }
}

Check this:

import java.util.*;
class Series 
{
    public static void main(String[] args) 
    {
    Scanner input=new Scanner(System.in);
    System.out.print("Enter the value of n: ");
    int n=input.nextInt();
    /*
    5+55+555+5555+....n
    5(1+11+111+1111)
    5(1+(1+10)+(1+100)+(1+1000))
    5(1+1+1+1+(10+100+1000))
    5(4+sum of series);
    a=10,r=10
    */

    int a=10,r=10;
    double p=Math.pow(r,n);
    double p1=10*(1-p);
    double p2=1-r;
    double sum=p1/p2;
    double result=5*(4+sum);
    System.out.println("Sum of series: "+sum);
    }
}

Hope that it will help you.