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 LIB;
using System;
using System.Linq;
using System.Text;
using System.Collections.Generic;

class Program
{
    public static IO IO = new IO();
    static void Main(string[] args)
    {
        long[] n = IO.LONG(' ');
        long o = 0;
        if (n[2] >= n[0] && n[2] <= n[1])
        {
            o = 1 + (n[1] - n[2]) / n[2];
        }
        else if (n[2] < n[0])
        {
            o = n[1] / n[2] - n[0] / n[2];
            if (n[0] % n[2] == 0) { o++; }
        }
        IO.WRITE(o);
        IO.FLUSH();
    }
}

namespace LIB
{
    public class IO
    {
        private const int WMAX = 1000;
        private StringBuilder S = new StringBuilder();
        private T R<T>(Func<string, T> f) { return f(Console.ReadLine()); }
        private T[] R<T>(Func<string, T> f, char c) { return STRING().Split(c).Select(f).ToArray(); }
        private T[] R<T>(Func<string, T> f, int l) { T[] r = new T[l]; for (int i = 0; i < l; i++) { r[i] = R(f); } return r; }
        private T[][] R<T>(Func<string, T> f, int l, char c) { T[][] r = new T[l][]; for (int i = 0; i < l; i++) { r[i] = R<T>(f, c); } return r; }
        private void W<T>(Func<T, string> f, T v, bool lf = true) { S.Append(f(v)); if (lf) { S.Append('\n'); } if (S.Length >= WMAX) { FLUSH(); } }
        public string STRING() { return R(s => s); }
        public string[] STRING(char c) { return R(s => s, c); }
        public string[] STRING(int l) { return R(s => s, l); }
        public string[][] STRING(int l, char c) { return R(s => s, l, c); }
        public int INT() { return R(int.Parse); }
        public int[] INT(char c) { return R(int.Parse, c); }
        public int[] INT(int l) { return R(int.Parse, l); }
        public int[][] INT(int l, char c) { return R(int.Parse, l, c); }
        public long LONG() { return R(long.Parse); }
        public long[] LONG(char c) { return R(long.Parse, c); }
        public long[] LONG(int l) { return R(long.Parse, l); }
        public long[][] LONG(int l, char c) { return R(long.Parse, l, c); }
        public double DOUBLE() { return R(double.Parse); }
        public double[] DOUBLE(char c) { return R(double.Parse, c); }
        public double[] DOUBLE(int l) { return R(double.Parse, l); }
        public double[][] DOUBLE(int l, char c) { return R(double.Parse, l, c); }
        public void WRITE(object s, bool lf = true) { W(v => v.ToString(), s, lf); }
        public void FLUSH() { Console.Write(S); S.Length = 0; }
    }
}