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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <algorithm>
#include <bitset>
#include <boost/dynamic_bitset.hpp>
#include <cfloat>
#include <cmath>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <typeindex>
#include <typeinfo>
#include <vector>

#define DEBUG(x) cout << #x << ": " << x << endl
#define INFILE() freopen("input.txt", "r", stdin)
#define REP(i, a, b) for (int i = (a); i < (b); i++)
#define REPC(i, a) REP(i, 0, a)
#define ALL(s) begin(s), end(s)
#define RALL(s) rbegin(s), rend(s)

using namespace std;

using ll = long long;
using ull = unsigned long long;
using i_i = pair<int, int>;
using ll_i = pair<ll, int>;
using i_ll = pair<int, ll>;
using d_i = pair<double, int>;
using ll_ll = pair<ll, ll>;
using d_d = pair<double, double>;

static constexpr ll LL_MOD = 1000000009;
static constexpr int I_MOD = 1000000007;
static constexpr double EPS = numeric_limits<double>::epsilon();
static constexpr double PI = 3.14159265358979323846264338327950288;

template <class T> static void scan(vector<T> &v);
static void scan(vector<string> &v, bool isWord = true);
static boost::dynamic_bitset<> scan(char trueValue = 'o');

int main(int argc, char *argv[]) {
	// INFILE();
  ll a, b, x;
  cin >> a >> b >> x;

  cout << (b / x) - ((a - 1) / x) + ((a == 0) ? 1 : 0) << endl;
  return 0;
}

template <class T> static void scan(vector<T> &v) {
  map<type_index, const char *const> m = {{typeid(int), "%d"},
                                          {typeid(ll), "%lld"},
                                          {typeid(double), "%lf"},
                                          {typeid(char), "%c"}};

  auto tFormat = m[typeid(T)];

  for (T &n : v) {
    scanf(tFormat, &n);
  }
}

static void scan(vector<string> &v, bool isWord) {
  if (isWord) {
    for (auto &n : v) {
      cin >> n;
    }
    return;
  }

  int i = 0, size = v.size();
  string s;
  getline(cin, s);

  if (s.size() != 0) {
    i++;
    v[0] = s;
  }

  for (; i < size; ++i) {
    getline(cin, v[i]);
  }
}

static boost::dynamic_bitset<> scan(char trueValue) {
  string s;
  getline(cin, s);

  if (s.size() == 0) {
    getline(cin, s);
  }

  for_each(begin(s), end(s),
           [trueValue](char &c) { c = (c == trueValue) ? '1' : '0'; });
  return boost::dynamic_bitset<>(string(rbegin(s), rend(s)));
}