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 Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.*;
import java.math.BigInteger;
// warm-up
// Always check the bounds
public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		BigInteger a=sc.nextBigInteger(), b=sc.nextBigInteger(), x=sc.nextBigInteger();
		if (b.divide(x).equals(a.divide(x))) System.out.println(0);
		else System.out.println(b.divide(x).subtract(a.divide(x)).add(BigInteger.ONE));
		sc.close();			
	}

	public static void main(String args[]) {
		solve();
	}

}