how to get atleast 50 points in eulersum? what is wrong in my approach? how to handle precission loss with Big-Integers?

i got AC in 2 subcases of TASK-1,i think this is due to precission loss,anything wrong with my approach?

my code->

class eulernumber {

public static void main(String[] args)

{
    Scanner sc=new Scanner(System.in);

    BigInteger n=new BigInteger("0");

    n=sc.nextBigInteger();

long ii=2;

    BigDecimal e=new BigDecimal("2.718281");

BigDecimal i=new BigDecimal(n);

    BigInteger l=BigInteger.ZERO;

   BigDecimal ll=e.add(i.subtract(BigDecimal.ONE).multiply(e));//find nth term of AP

l=e.add(ll).toBigInteger(); fing sum of nth and first term

BigDecimal bb=new BigDecimal(l);

   System.out.println(i.divide(BigDecimal.valueOf(ii)).multiply(bb).toBigInteger()); //find sum of nth term of AP

}

}