Problem:
Score : 300 points

Problem Statement

Given any integer x, Aoki can do the operation below.

Operation: Replace x with the absolute difference of x and K.

You are given the initial value of an integer N. Find the minimum possible value taken by N after Aoki does the operation zero or more times.

Constraints

0 ≤ N ≤ 10^{18}

1 ≤ K ≤ 10^{18}

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the minimum possible value taken by N after Aoki does the operation zero or more times.

Sample Input 1

7 4

Sample Output 1

1

Initially, N=7.

After one operation, N becomes |7-4| = 3.

After two operations, N becomes |3-4| = 1, which is the minimum value taken by N.

Sample Input 2

2 6

Sample Output 2

2

N=2 after zero operations is the minimum.

Sample Input 3

1000000000000000000 1

Sample Output 3

0

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"sort"
	"strconv"
	"strings"
	"unsafe"
)

var (
	sc scanner
)

func main() {
	n, k := sc.nextInt(), sc.nextInt()
	fmt.Println(min(n%k, abs(n%k-k)))
}

/* template functions */

func init() {
	sc = scanner{
		buf: make([]string, 0, 10000),
		cur: 0,
		r:   bufio.NewReader(os.Stdin),
	}
}

type scanner struct {
	buf []string
	cur int
	r   *bufio.Reader
}

func (s *scanner) readln() {
	rbuf := make([]byte, 0, 100)
	for {
		line, prefix, err := s.r.ReadLine()
		if err != nil {
			panic(err)
		}
		rbuf = append(rbuf, line...)
		if prefix == false {
			break
		}
	}
	s.cur = 0
	s.buf = strings.Split(*(*string)(unsafe.Pointer(&rbuf)), " ")
}

func (s *scanner) isFull() bool {
	if s.cur == len(s.buf) {
		return true
	}
	return false
}

func (s *scanner) resetCur() {
	s.cur = 0
}

func (s *scanner) next() string {
	if s.cur == 0 {
		s.readln()
	}
	res := s.buf[s.cur]
	s.cur++
	if s.isFull() {
		s.resetCur()
	}
	return res
}

func (s *scanner) nexts() []string {
	s.readln()
	s.resetCur()
	return s.buf
}

func (s *scanner) nextByte() byte {
	if s.cur == 0 {
		s.readln()
	}
	res := s.buf[s.cur][0]
	s.cur++
	if s.isFull() {
		s.resetCur()
	}
	return res
}

func (s *scanner) nextInt() int {
	if s.cur == 0 {
		s.readln()
	}
	res, _ := strconv.Atoi(s.buf[s.cur])
	s.cur++
	if s.isFull() {
		s.resetCur()
	}
	return res
}

func (s *scanner) nextInts() []int {
	s.readln()
	res := make([]int, len(s.buf))
	for i, _ := range s.buf {
		res[i], _ = strconv.Atoi(s.buf[i])
	}
	s.resetCur()
	return res
}

func (s *scanner) nextFloat() float64 {
	if s.cur == 0 {
		s.readln()
	}
	res, _ := strconv.ParseFloat(s.buf[s.cur], 64)
	s.cur++
	if s.isFull() {
		s.resetCur()
	}
	return res
}

func (s *scanner) nextFloats() []float64 {
	s.readln()
	res := make([]float64, len(s.buf))
	for i, _ := range s.buf {
		res[i], _ = strconv.ParseFloat(s.buf[i], 64)
	}
	s.resetCur()
	return res
}

func max(x, y int) int {
	return int(math.Max(float64(x), float64(y)))
}

func min(x, y int) int {
	return int(math.Min(float64(x), float64(y)))
}

func abs(x int) int {
	return int(math.Abs(float64(x)))
}

// Searchable
// idx := lower_bound([]int{-199, -1, 0, 2, 4, 67, 100, 8435}, 60)
// => idx = 5
//
// No present
// idx := lower_bound([]int{-199, -1, 0, 2, 4, 67, 100, 8435}, 10000)
// => idx = 8

func lower_bound(a []int, x int) int {
	return sort.SearchInts(a, x)
}

func dump(value ...interface{}) {
	for _, v := range value {
		fmt.Fprintf(os.Stderr, "%#v\n", v)
	}
}

func yes() {
	fmt.Println("Yes")
}

func no() {
	fmt.Println("No")
}