##### 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.

umm, how do you solve?

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.

Agreed! (Also remember that BRACKETS MATTER)!

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.