### 2009 Canadian Computing Competition, Stage 1

## Problem J1: ISBN

The International Standard Book Number (ISBN) is a 13-digit code for identifying books. These numbers have a special property for detecting whether the number was written correctly.

The 1-3-sum of a 13-digit number is calculated by multiplying the digits alternately by 1's and 3's (see example) and then adding the results. For example, to compute the 1-3-sum of the number 9780921418948 we add

9×1 + 7×3 + 8×1 + 0×3 + 9×1 + 2×3 + 1×1 + 4×3 + 1×1 + 8×3 + 9×1 + 4×3 + 8×1

to get 120.

The special property of an ISBN number is that its 1-3-sum is always a multiple of 10.

Write a program to compute the 1-3-sum of a 13-digit number. To reduce the amount of typing, you may assume that the first ten digits will always be 9780921418, like the example above. Your program should input the last three digits and then print its 1-3-sum.

### Sample Input

9 4 8

### Sample Output

The 1-3-sum is 120

### Sample Input 2

0 5 2

### Sample Output 2

The 1-3-sum is 108

All Submissions

Best Solutions

**Point Value:** 3

**Time Limit:** 2.00s

**Memory Limit:** 16M

**Added:** May 14, 2009

**Languages Allowed:**

C++03, PAS, C, HASK, ASM, RUBY, PYTH2, JAVA, PHP, SCM, CAML, PERL, C#, C++11, PYTH3

## Comments (Search)

eraj4evaon Nov 21, 2013 - 1:14:20 am UTC Confusionbbi5291on Nov 21, 2013 - 9:12:00 am UTC Re: Confusion