Problem:
Score : 200 points

Problem Statement

You are given nonnegative integers a and b (a ≤ b), and a positive integer x.
Among the integers between a and b, inclusive, how many are divisible by x?

Constraints

0 ≤ a ≤ b ≤ 10^{18}

1 ≤ x ≤ 10^{18}

Input

The input is given from Standard Input in the following format:

a b x

Output

Print the number of the integers between a and b, inclusive, that are divisible by x.

Sample Input 1

4 8 2

Sample Output 1

3

There are three integers between 4 and 8, inclusive, that are divisible by 2: 4, 6 and 8.

Sample Input 2

0 5 1

Sample Output 2

6

There are six integers between 0 and 5, inclusive, that are divisible by 1: 0, 1, 2, 3, 4 and 5.

Sample Input 3

9 9 2

Sample Output 3

0

There are no integer between 9 and 9, inclusive, that is divisible by 2.

Sample Input 4

1 1000000000000000000 3

Sample Output 4

333333333333333333

Watch out for integer overflows.

Solution in C# (Mono 4.6.2.0) (judge verdict: Time Limit Exceeded)

using System;
using System.IO;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;

namespace Paiza
{
	class MainClass
	{
		public static void Main(string[] args)
		{
			string[] str = Console.ReadLine().Split(' ');
			ulong a = Convert.ToUInt64(str[0]);
			ulong b = Convert.ToUInt64(str[1]);
			ulong c = Convert.ToUInt64(str[2]);
			if(a % c != 0)
			{
				//ulong a = c - a
				ulong i = 0;
				for(;;)
				{

					if((a+i) % c == 0)
					break;
					i++;
				}
				a = a + i;
			}
			if(b % c != 0)
			{
				ulong i = b;
				for(;;)
				{

					if((b - i) % c == 0)
					break;
					i--;
				}
				b = i;
			}
			ulong dlt = b - a;
			ulong answer = dlt / c + 1;

			if(a > b)
				answer = 0;
			Console.WriteLine(answer);
		}
	}
}