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 {
        (a - 1) / x + 1
    } else {
        0
    }
}

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

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