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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

long K = 0;

long f(long x) { return labs(x - K); }

int main()
{
  char in[1000];
  fgets(in, 1000, stdin);
  
  long x = atoi(strtok(in," "));
  K = atoi(strtok(NULL, " "));
  
  if(x == 0) { printf("%ld", K); return 0; }
  if(x == K) { printf("0"); return 0; }
  
  long old = x;
  long next = f(x);
  for(; old >= next; next = f(next)) { /*printf("%ld %ld\n", old, next);*/ old = next; }
  
  printf("%ld", old);
  return 0;
}