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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
 
class Program
{
    static void Main(string [] args)
    {
        var rl = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToList();
        var a = rl[0] % rl[2] == 0 ? rl[0] : rl[0] + (rl[2] - rl[0] % rl[2]);
        var b = rl[1] - rl[1] % rl[2];
        if (a > b)
        {
            Console.WriteLine("0");
        }
        else
        {
            Console.WriteLine(b / rl[2] - a / rl[2] + 1);
        }
    }
}