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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace test48b
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] str = Console.ReadLine().Split(' ');
            long ifrom = long.Parse(str[0]);
            long ito = long.Parse(str[1]);
            long iwaru = long.Parse(str[2]);

            long icnt = Cal(ifrom, ito, iwaru);

            Console.WriteLine(icnt);
            
        }

        private static long Cal(long ifrom, long ito, long iwaru)
        {
            long icnt = 0;
            long[] itbl = new long[3];

            itbl[0] = ifrom;
            itbl[1] = ito;

            if (ifrom <iwaru)
            {
                itbl[0] = iwaru;
            }
            itbl[2] = (itbl[1] - itbl[0])+1;

            double d1 = itbl[2] / iwaru;
            double d2 = itbl[2] % iwaru;
            if (d2 > 0)
            {
                icnt = Convert.ToInt64(Math.Ceiling(d1));
            }
            else
            {
                icnt = Convert.ToInt64(d1);
            }

            if (ifrom == 0 && iwaru != 1)
            {
                icnt++;
            }

            return icnt;
        }
    }
}