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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Applicative

main :: IO ()
main = do
  { [a,b,x] <- readLineInputs :: IO [Int]
  ; print $ solve a b x
  }
; 
solve :: Int -> Int -> Int -> Int
solve a b x = let
  { r = a `mod` x
  ; d = b - a + 1 - if r == 0 then 0 else x - r 
  } in if d < 0 then 0 else case divMod d x of
          { (q,0) -> q; (q,_) -> q+1 }

-- I/O

readLineInputs :: Read a => IO [a]
readLineInputs = map read . words <$> getLine