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 static System.Console;
using static System.Math;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TemplateAlgorithm
{
    class Program
    {
        public const long Inf = (long)1e18;
        public const double eps = 1e-6;
        public const string alfa = "abcdefghijklmnopqrstuvwxyz";
        public const string ALFA = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        public const int MOD = 1000000007;
        
        // c ot i
        static int ToInt(char c) => c - '0';

        static void Main(string[] args)
        {
            string[] str = Console.ReadLine().Split(' ');
            long a = long.Parse(str[0]);
            long b = long.Parse(str[1]);
            long n = long.Parse(str[2]);
            long ans = b / n - a / n;
            if (a % n == 0) ans++;
            Console.WriteLine(ans);
        }

        #region  範囲

        public static bool InRange<T>(T begin, T end, T value) where T : IComparable<T> 
            => value.CompareTo(begin) >= 0 && value.CompareTo(end) <= 0;

        #endregion

        #region MIN,MAX

        /// <summary>
        /// 最大値を返す
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="vals"></param>
        /// <returns></returns>
        public static T MaxValue<T>(params T[] vals) => vals.Max();

        /// <summary>
        /// 最小値を返す
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="vals"></param>
        /// <returns></returns>
        public static T MinValue<T>(params T[] vals) => vals.Min();
        #endregion
    }

    #region IO

    /// <summary>
    /// IO
    /// </summary>
    public class IO
    {
        public static string ReadStr(bool isTrim = false) => (isTrim) ? ReadLine().Trim() : ReadLine();
        public static int ReadInt() => int.Parse(ReadStr());

        public static long ReadLong() => long.Parse(ReadStr());

        public static decimal ReadDecimal() => decimal.Parse(ReadStr());
        public static double ReadDouble() => double.Parse(ReadStr());
        public static string[] ReadStrArr(char separator = ' ') => ReadLine().Split(separator);
        public static int[] ReadIntArr() => Array.ConvertAll(ReadStrArr(), int.Parse);
        public static long[] ReadLongArr() => Array.ConvertAll(ReadStrArr(), long.Parse);

        public static decimal[] ReadDecimalArr() => Array.ConvertAll(ReadStrArr(), decimal.Parse);
        public static double[] ReadDoubleArr() => Array.ConvertAll(ReadStrArr(), double.Parse);        
    }

    #endregion    
}