Problem With BigInt

package lightoj;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import static java.lang.System.out;
import java.math.BigInteger;
import java.util.Scanner;
import java.util.StringTokenizer;

public class LightOJ {


    static BigInteger fn(int a,int b, int c, int d, int e, int f, int n)
    {
        BigInteger Big_a = BigInteger.valueOf(a);
        BigInteger Big_b = BigInteger.valueOf(b);
        BigInteger Big_c = BigInteger.valueOf(c);
        BigInteger Big_d = BigInteger.valueOf(d);
        BigInteger Big_e = BigInteger.valueOf(e);
        BigInteger Big_f = BigInteger.valueOf(f);

        BigInteger Big_1 = BigInteger.valueOf(n-1);
        BigInteger Big_2 = BigInteger.valueOf(n-2);
        BigInteger Big_3 = BigInteger.valueOf(n-3);
        BigInteger Big_4 = BigInteger.valueOf(n-4);
        BigInteger Big_5 = BigInteger.valueOf(n-5);
        BigInteger Big_6 = BigInteger.valueOf(n-6);

        BigInteger Big_Sum = BigInteger.valueOf(0);
        BigInteger Big_Reminder =new BigInteger("10000007");





    if (n == 0) return Big_a;
    if (n == 1) return Big_b;
    if (n == 2) return Big_c;
    if (n == 3) return Big_d;
    if (n == 4) return Big_e;
    if (n == 5) return Big_f;


    for(int i=0;i<=n;i++)
     Big_Sum = Big_Sum.add(Big_1).add(Big_2).add(Big_3).add(Big_4).add(Big_5).add(Big_6);


    return Big_Sum;


    }

    public static void main(String[] args) throws Exception{
        FastReader scan = new FastReader();
          int n,cases,a,b,c,d,e,f;;
          cases = scan.nextInt();
        for (int caseno = 1; caseno <= cases; ++caseno) {
        a = scan.nextInt();
        b = scan.nextInt();
        c = scan.nextInt();
        d = scan.nextInt();
        e = scan.nextInt();
        f = scan.nextInt();
        n = scan.nextInt();
        System.out.println("Case "+caseno+": "+fn(a,b,c,d,e,f,n));
    }
      //% 10000007
      //  int N = 20;

    }


    private static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }
        String next()
        {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                }
                catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() { return Integer.parseInt(next()); }

        long nextLong() { return Long.parseLong(next()); }

        double nextDouble(){ return Double.parseDouble(next()); }

        String nextLine()
        {
            String str = "";
            try {
                str = br.readLine();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

}