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# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;

namespace ABC048B
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine().Split(' ');
            var a = long.Parse(input[0]);
            var b = long.Parse(input[1]);
            var x = long.Parse(input[2]);
            if (a == b)
            {
                Console.WriteLine(0);
                return;
            }
            else if (a == 0)
            {
                var answer = (b / x) + 1;
                Console.WriteLine(answer);
            }
            else
            {
                var answer = (b / x) - ((a - 1) / x);
                Console.WriteLine(answer);
            }
        }
    }
}