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 (Clang 10.0.0) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#pragma warning(disable : 4996)

int main()
{

    long long a, b, x;
    long long count = 0;

    scanf("%lld %lld %lld", &a, &b, &x);

    long long ai = a / x;
    long long bi = b / x;

    long long start, goal;

    if (ai * x == a)
        start = ai;
    else
        start = ai + 1;

    goal = bi;

    printf("%lld", goal - start + 1);


    return 0;

}