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<bits/stdc++.h>

using namespace std;
using ll = long long int;

#define loop(i, n) for(int i = 0;i < n;i++)
#define vi vector<int>
#define vvi vector<vi>
#define IINF 2e9;
#define MOD 1e9+7;

int main(void){

  ll a, b, x;
  cin >> a >> b >> x;
  
  ll ans1, ans2;
  if(a == 0) ans1 = 0;
  else ans1 = (a-1)/x;
  
  if(b == 0) ans2 = 0;
  else ans2 = (b-1)/x;
  
  cout << ans2 - ans1 << endl;
}