Problem:
Score : 100 points

Problem Statement

You went shopping to buy cakes and donuts with X yen (the currency of Japan).

First, you bought one cake for A yen at a cake shop.
Then, you bought as many donuts as possible for B yen each, at a donut shop.

How much do you have left after shopping?

Constraints

1 \leq A, B \leq 1 000

A + B \leq X \leq 10 000

X, A and B are integers.

Input

Input is given from Standard Input in the following format:

X
A
B

Output

Print the amount you have left after shopping.

Sample Input 1

1234
150
100

Sample Output 1

84

You have 1234 - 150 = 1084 yen left after buying a cake.
With this amount, you can buy 10 donuts, after which you have 84 yen left.

Sample Input 2

1000
108
108

Sample Output 2

28

Sample Input 3

579
123
456

Sample Output 3

0

Sample Input 4

7477
549
593

Sample Output 4

405

Solution in Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

add_b :: Int -> Int -> Int
add_b x b
    | x < b = 0
    | otherwise = add_b x (b * 2) + 1

main = do
    
    xs <- getLine
    as <- getLine
    bs <- getLine

    let a = read as
        b = read bs
        x = read xs
    
    print $ x - a - ((add_b (x - a) b) * b)