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 JavaScript (node.js v5.12) (judge verdict: Runtime Error)

'use strict'
const main = arg => {
	const input = arg.trim().split("\n");
	let a = input[0].split(' ').map(n => BigInt(n))[0]
	let b = input[0].split(' ').map(num => BigInt(num))[1]
	let x = input[0].split(' ').map(num => BigInt(num))[2]
	let left = b / x * x / x
	let right = (divCeil(a, x) * x) / x
	if(a <= x) {
		console.log((b / x).toString())
		return
	}
	console.log( (left - right + BigInt(1)).toString())

	function divCeil (a, x) {
		if((a % x) * BigInt(2) >= x) {
			return a / x + BigInt(1)
		}
		return a / x
	}
}   
main(require('fs').readFileSync('/dev/stdin', 'utf8'));