##### Canadian Computing Competition: 2009 Stage 1, Junior #1

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 perform:

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

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. Use a format similar to the samples below.

#### Sample Input 1

```
9
4
8
```

#### Sample Output 1

`The 1-3-sum is 120`

#### Sample Input 2

```
0
5
2
```

#### Sample Output 2

`The 1-3-sum is 108`

## Comments

My PY3 code gives me a type error but in another tab it gives the proper output. I'm not sure what the problem is.

Can anyone tell me how to calculate the ISBN number? 0 times 3 + 5 + 2 times 3 is obviously not 108!

This comment is hidden due to too much negative feedback. Show it anyway.

You have to write the full sentence

Oh. I forgot the sentence.

Note that your output must exactly be the same as specified.

`The 1-3-sum is 120`

is fine, but`120`

is wrong, and`The 1-3-sum is 120.`

(notice the period) is also wrong.Agreed! (Also remember that BRACKETS MATTER)!