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: Wrong Answer)

using System;

namespace atcoder_ABC048B
{
    class MainClass
    {
        public static void Main(string[] args)
        {
			string[] array = Console.ReadLine().Split(' ');
			ulong startNumber = ulong.Parse(array[0]);
			ulong endNumber = ulong.Parse(array[1]);
			ulong x = ulong.Parse(array[2]);

			ulong result1 = endNumber / x;

			ulong result2 = 0;
			if (startNumber != 0)
			{
				result2 = (startNumber - 1) / x;
			}
			//for (ulong i = startNumber; i <= endNumber; i++)
			//{
			//	if (i % x == 0) resultCount++;
			//}

			Console.WriteLine(result1 - result2);
        }
    }
}