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<vector>
#include<algorithm>
#include<cctype>
#include<utility>
#include<string>

#define REP(n) for(int i = 0;i < n;i++)
#define LLREP(n) for(long long int  i = 0;i < n;i++)
typedef long long int ll;
typedef unsigned long long int ull;
using namespace std;
#define MAX_A 1000000007

ll f(ll n,ll x){

    if(n == -1){
        return 0;
    }else{
        return (n/x);
    }
}


int main(){

    ll a,b,x;
    cin >> a >> b >> x;

    ll f_a = f(a-1,x);
    ll f_b = f(b,x);
    //cout << f_a << " " << f_b << endl;

    cout << f_b-f_a << endl;


    return 0;
}