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: Accepted)

<?php
fscanf(STDIN,'%d%d%d',$A,$B,$X);
$P=$A%$X;
$Q=$B%$X;
$T=($B-$Q-$A+$P)/$X;
if($A==$B){
  if($P==0){
    echo 1;
  }else{
    echo 0;
  }
}else{
  if($P==0){
    echo $T+1;
  }else{
    echo $T;
  }
}
echo "\n";

 ?>