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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class MainClass
{
    static void Main(string[] args)
    {
		AnswerA();
    }
	public static void AnswerA()
    {
      int X = int.Parse(Console.ReadLine());
      int A = int.Parse(Console.ReadLine());
      int B = int.Parse(Console.ReadLine());
      X -= A;//ケーキは固定で１個購入
      int CanBuyBCnt = (int)Math.Floor((decimal)X / (decimal)B);
      X -= (CanBuyBCnt * B);
      Console.WriteLine(X.ToString());
    }
}