This is my solution

package hackerrankcode;

import java.io.; import java.math.BigInteger; import java.util.;

public class Repeated_String {

public static BigInteger repeat(String s,long n){

    BigInteger min = new BigInteger("9223372036854775808");

    BigInteger increment = new BigInteger("1");

    List<Character> list=new ArrayList<>();

    for(long i=0;i<s.length();i++){

        list.add(s.charAt((int)i));

    }

    //System.out.println("The list is: "+list);

    if(list.contains("a")){

       // System.out.println("output from here");

        BigInteger bigInteger=new BigInteger("0");

        return bigInteger;

    }else if(n>=list.size() && n<=Math.pow(10, 6)){

        int y=0;

        while(list.size()!=n){

            list.add(s.charAt(y));

            y++;

            if(y==s.length()){

                y=0;

            }

        }

    }else{

    BigInteger a = min.add(increment);    

        BigInteger bigInteger=new BigInteger(String.valueOf(n));

      //  System.out.println("Output from else");

        return a;

    }
     int a=0;

     //System.out.println("The list2 is: "+list);

    for(Character i:list){

        if(i=='a'){

            a++;

        }

    }

    BigInteger bigInteger=new BigInteger(String.valueOf(a));

    return bigInteger;

}

public static void main(String[] args) {

Scanner scanner=new Scanner(System.in);    

String repeatedString;
long n;

    System.out.println("Enter your string: ");
    repeatedString=scanner.nextLine();

    System.out.println("Enter your number: ");
    n=scanner.nextLong();

    System.out.println(""+String.valueOf(repeat(repeatedString,n)));

}}

}

//}