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: Runtime Error)

#include <bits/stdc++.h>
#define ll  long long

#ifdef LOCAL
    #define eprintf(...) fprintf(stderr, "\e[31;1m"); fprintf(stderr, __VA_ARGS__); fprintf(stderr, "\e[0m")
#else
    #define eprintf(...) 42
#endif

ll f(ll X, ll n)
{
    if (-1 == n)
    {
        return 0;
    }
    return (n / X + 1);
}

ll solve(const int A, const int B, const int X)
{
    int a = f(X, A - 1);
    int b = f(X, B);
    return b - a;
}

int main(void)
{
    int A, B, X;
    std::cin >> A >> B >> X;
    std::cout << solve(A, B, X) << std::endl;

    return 0;
}