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 Rust (1.15.1) (judge verdict: Accepted)

fn calc(n: i64, x: i64) -> i64 {
    if n < 0 {
        return 0;
    }

    n / x + 1
}

fn main() {
    let (a, b, x) = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).ok();
        let abx: Vec<i64> = buf
            .trim()
            .split_whitespace()
            .map(|e| e.trim().parse().ok().unwrap())
            .collect();
        (abx[0], abx[1], abx[2])
    };

    let ans = calc(b, x) - calc(a - 1, x);
    println!("{}", ans);
}