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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	fsc := NewFastScanner()
	A, B, X := fsc.NextInt64(), fsc.NextInt64(), fsc.NextInt64()
	var result int64
	result = B / X
	if A != 0 {
		A--
	}
	result -= A / X
	fmt.Println(result)
}

//template
type FastScanner struct {
	r   *bufio.Reader
	buf []byte
	p   int
}

func NewFastScanner() *FastScanner {
	rdr := bufio.NewReaderSize(os.Stdin, 1024)
	return &FastScanner{r: rdr}
}
func (s *FastScanner) Next() string {
	s.pre()
	start := s.p
	for ; s.p < len(s.buf); s.p++ {
		if s.buf[s.p] == ' ' {
			break
		}
	}
	result := string(s.buf[start:s.p])
	s.p++
	return result
}
func (s *FastScanner) NextLine() string {
	s.pre()
	start := s.p
	s.p = len(s.buf)
	return string(s.buf[start:])
}
func (s *FastScanner) NextInt() int {
	v, _ := strconv.Atoi(s.Next())
	return v
}
func (s *FastScanner) NextInt64() int64 {
	v, _ := strconv.ParseInt(s.Next(), 10, 64)
	return v
}

func (s *FastScanner) pre() {
	if s.p >= len(s.buf) {
		s.readLine()
		s.p = 0
	}
}
func (s *FastScanner) readLine() {
	s.buf = make([]byte, 0)
	for {
		l, p, e := s.r.ReadLine()
		if e != nil {
			panic(e)
		}
		s.buf = append(s.buf, l...)
		if !p {
			break
		}
	}
}

//Max,Min
func IntMax(a, b int) int {
	if a < b {
		return b
	}
	return a
}

func Int64Max(a, b int64) int64 {
	if a < b {
		return b
	}
	return a
}
func Float64Max(a, b float64) float64 {
	if a < b {
		return b
	}
	return a
}

func IntMin(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func Int64Min(a, b int64) int64 {
	if a > b {
		return b
	}
	return a
}
func Float64Min(a, b float64) float64 {
	if a > b {
		return b
	}
	return a
}

//Gcd
func IntGcd(a, b int) int {
	if a < b {
		b, a = a, b
	}
	if b == 0 {
		return a
	}
	return IntGcd(b, a%b)
}
func Int64Gcd(a, b int64) int64 {
	if a < b {
		b, a = a, b
	}
	if b == 0 {
		return a
	}
	return Int64Gcd(b, a%b)
}

func IntAbs(a int) int {
	if a < 0 {
		a *= -1
	}
	return a
}

func Int64Abs(a int64) int64 {
	if a < 0 {
		a *= -1
	}
	return a
}