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.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace NotFounds
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            new Program().Solve(new MyInputStream(Console.In, ' '));
            Console.Out.Flush();
        }

        public void Solve(MyInputStream cin)
        {
            var x = cin.ReadInt();
            var a = cin.ReadInt();
            var b = cin.ReadInt();
            WriteLine((x - a) % b);
        }
    }

    public class MyInputStream
    {
        private readonly System.IO.TextReader _stream;
        private char separator = ' ';
        private Queue<string> inputStream;
        public MyInputStream(System.IO.TextReader s, char separator = ' ')
        {
            this.separator = separator;
            this._stream = s;
            inputStream = new Queue<string>();
        }
        public string Read()
        {
            if (inputStream.Count != 0) return inputStream.Dequeue();
            string[] tmp = _stream.ReadLine().Split(separator);
            for (int i = 0; i < tmp.Length; ++i)
                inputStream.Enqueue(tmp[i]);
            return inputStream.Dequeue();
        }
        public string ReadLine() { return _stream.ReadLine(); }
        public int ReadInt() { return int.Parse(Read()); }
        public long ReadLong() { return long.Parse(Read()); }
        public double ReadDouble() { return double.Parse(Read()); }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read(); return ret;}
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt(); return ret;}
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong(); return ret;}
    }
}