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: Accepted)

#include <bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define sz size()
#define all(a) a.begin(), a.end()
#define allr(a) a.rbegin(), a.rend()
#define mod 1000000007
#define forn(i, n) for (int i = 0; i < (int) (n); ++i)
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)

using namespace std;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    unsigned long long int a,b,d;
    cin >> a >> b >> d;
    b /= d;
    a = (a<1)?(a/d)-1:(a-1)/d;
    unsigned long long int c = (unsigned long long int)b - (unsigned long long int)a;
    cout << c;
    return 0;
}