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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php
fscanf(STDIN, "%s %s %s", $a, $b, $x);
$s = big_floor($a, $x);
if ($a % $x) $s++;
$t = big_floor($b, $x);
echo $t - $s + 1;

function big_floor($a, $b) {
	$c = sprintf("%.0f", floor($a / $b));
	if (strlen($c) <= 14) {
		return $c;
	}
	$c = null;
	while (strlen($a) > 10) {
		$a1 = substr($a, 0, 10);
		$a = substr($a, 10);
		$c .= floor($a1 / $b);
		$m = $a1 % $b;
		if ($m) $a = $m . $a;
	}
	$c .= floor($a / $b);
	return $c;
}