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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        public static void Main()
        {
            int X = int.Parse(Console.ReadLine());
            int A = int.Parse(Console.ReadLine());
            int B = int.Parse(Console.ReadLine());
            if (0 <= A && A <= 1000 && 0 <= B && B <= 1000 && A + B <= X && X <= 10000)
            {
                X -= A;
                if (X >= B)
                {
                    while (true)
                    {
                        X -= B;
                        if (X <= B)
                        {
                            break;
                        }
                    }
                }
            }

            Console.WriteLine("{0}", X);
        }
    }
}