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;
using System.Linq;
using System.IO;
using System.Text;
using System.Collections;
using System.Collections.Generic;
 
class Program
{
    static void Main()
    {
        ulong[] inputs = Console.ReadLine().Split(' ')
                                    .Select(val => ulong.Parse(val))
                                    .ToArray();
        if(inputs[1] < inputs[2])
        {
            Console.WriteLine(0);
            return;
        }
        ulong cnt = 0;
        ulong i = 0;
        for (i = inputs[0]; i < inputs[1];)
        {
            ulong mod = i % inputs[2];
            if(mod == 0) {cnt++; break;}
            else i += inputs[2] - mod;
        }
        cnt = (inputs[1] - i) / inputs[2];
        Console.WriteLine(cnt);
    }
}