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;

class Program
{
 static void Main(string[] args)
 {
   string[] input = Console.ReadLine().Split(' ');
   
   long a = long.Parse(input[0]);
   long b = long.Parse(input[1]);
   long x = long.Parse(input[2]);
   long num1 = 0;
   long num2 = 0;
   long calc = 0;
   
   num1 = a / x;
   num2 = b / x;
   
   if( (a%x) == 0 )
   {
     calc = (num2 - num1) + 1;
   }
   else
   {
     calc = (num2 - num1);
   }
   
   Console.WriteLine(calc);
 }
}