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)

#![allow(unused, non_snake_case, dead_code, non_upper_case_globals)]
use std::cmp::*;
use std::collections::*;
use std::mem::*;

fn main() {
    let (r, w, e) = (std::io::stdin(), std::io::stdout(), std::io::stderr());
    let mut io = IO::new(r.lock(), w.lock(), e.lock());
    assert_eq!(!0usize, std::usize::MAX); //🙊

    let (a, b, x) = (io.read::<i64>(), io.read::<i64>(), io.read::<i64>());

    if a == b {
        io.writeln(if a % x == 0 { 1 } else { 0 });
        return;
    }
    if a == 0 {
        io.writeln(b / x + 1);
        return;
    }
    io.writeln(b / x - (a - 1) / x);
}

static MOD: i64 = 1000000007;
static INF: i64 = std::i64::MAX >> 1;
// IO
use std::io::*;
struct IO<R: Read, W: Write, E: Write> {
    Read: R,
    Write: BufWriter<W>,
    Error: BufWriter<E>,
}
impl<R: Read, W: Write, E: Write> IO<R, W, E> {
    fn new(r: R, w: W, e: E) -> IO<R, W, E> {
        IO {
            Read: r,
            Write: BufWriter::new(w),
            Error: BufWriter::new(e),
        }
    }
    fn read<T>(&mut self) -> T
    where
        T: std::str::FromStr,
    {
        let next: String = self
            .Read
            .by_ref()
            .bytes()
            .map(|c| c.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect();
        next.parse().ok().unwrap()
    }
    fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
    fn chari(&mut self) -> Vec<i64> {
        self.chars()
            .iter()
            .map(|&c| (c as u8 - b'0') as i64)
            .collect::<Vec<i64>>()
    }
    fn readn<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read::<T>()).collect::<Vec<_>>()
    }
    fn readmat<T: std::str::FromStr>(&mut self, n: usize, m: usize) -> Vec<Vec<T>> {
        (0..n).map(|_| self.readn(m)).collect()
    }
    fn write<S: ToString>(&mut self, val: S) {
        self.Write.write(val.to_string().as_bytes());
    }
    fn writeln<S: ToString>(&mut self, val: S) {
        self.Write.write(val.to_string().as_bytes());
        self.Write.write(b"\n");
    }
    fn debug<S: std::fmt::Debug>(&mut self, val: S) {
        writeln!(self.Error, "(debug) {:?}", &val);
    }
    fn debug2<S: std::fmt::Debug, T: std::fmt::Debug>(&mut self, val1: S, val2: T) {
        writeln!(self.Error, "(debug2) {:?} -> {:?}", val1, val2);
    }
    fn debug3<S: std::fmt::Debug, T: std::fmt::Debug, U: std::fmt::Debug>(
        &mut self,
        val1: S,
        val2: T,
        val3: U,
    ) {
        writeln!(
            self.Error,
            "(debug3) {:?} -> {:?} -> {:?}",
            val1, val2, val3
        );
    }
}