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 divisors(a: i64, x: i64) -> i64 {
    if a < 0 {
        0
    } else {
        a / x + 1
    }
}

fn solve(a: i64, b: i64, x: i64) -> i64 {
    divisors(b, x) - divisors(a - 1, x)
}

fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let mut iter = s.split_whitespace().map(|w| w.trim().parse().ok().unwrap());
    let a = iter.next().unwrap();
    let b = iter.next().unwrap();
    let x = iter.next().unwrap();
    let ans = solve(a, b, x);
    println!("{}", ans);
}