7733


int sum = 0;
            int dd;

            for ( int i = 0; i < d.length; i++ )
            {
              // Is right-to-left position even?
              if ( i % 2 == 0 )
              {
                // If it is, set dd to twice the digit
                dd = 2 * d[i];

                // Add the sum of dd's digits to sum
                int tempsum = 0;
                while (dd != 0) {
                    tempsum += dd;
                    dd /= 10;
                }
                sum += tempsum ;
              }
              else
              {
                // If right-to-left position is odd,
                // add the digit to sum
                sum += d[i];
              }
            }

            valid = (sum % 10 == 0);



int sum = 0;
            int dd;

            for ( int i = 0; i < e.length; i++ )
            {
              if((e.length - i) % 2 != 0)
              {
                dd = 2 * e[i];
                sum += ((dd % 10) + (dd / 10));
              }
              else
                sum += e[i];
            }

            checkdigit = (((sum / 10) + 1) * 10) - sum;

        if(checkdigit >= 10)
        checkdigit %= 10;