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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <stdio.h>       // printf,scanf
#include <stdlib.h>
#include <math.h>
#include <string>
#include <vector>
#include <algorithm>  //sort,binarySearch
#include <functional> 
#include <iomanip>    // setprecision
#include <utility>    // c+11 Array
#include <set>
#include <sstream>
#include <map>
#include <bits/stdc++.h>
#define MOD (1e+9)+7
#define PI 3.141592653589793238462643383279
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define pb(x) push_back(x)
#define debug(x) cerr << #x << " = " << x << endl;
#define debret(x) debug(x) ; return 0;

using namespace std;

int main(){

    long long int a;
    long long int b;
    long long int c;
    long long int ans = 0;
    cin >> a >> b >> c;

    if(b < c){
        cout << 0 << endl;
        return 0;
    }
    ans += b / c;
    if(a != 0){
        ans -= (a-1) / c;
    }else{
        ans++;
    }
    cout << ans << endl;
    return 0;
}