Problem:
Score : 300 points

Problem Statement

There is a circular pond with a perimeter of K meters, and N houses around them.

The i-th house is built at a distance of A_i meters from the northmost point of the pond, measured clockwise around the pond.

When traveling between these houses, you can only go around the pond.

Find the minimum distance that needs to be traveled when you start at one of the houses and visit all the N houses.

Constraints

2 \leq K \leq 10^6

2 \leq N \leq 2 \times 10^5

0 \leq A_1 < ... < A_N < K

All values in input are integers.

Input

Input is given from Standard Input in the following format:

K N
A_1 A_2 ... A_N

Output

Print the minimum distance that needs to be traveled when you start at one of the houses and visit all the N houses.

Sample Input 1

20 3
5 10 15

Sample Output 1

10

If you start at the 1-st house and go to the 2-nd and 3-rd houses in this order, the total distance traveled will be 10.

Sample Input 2

20 3
0 5 15

Sample Output 2

10

If you start at the 2-nd house and go to the 1-st and 3-rd houses in this order, the total distance traveled will be 10.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.*;
public class Main {
  
  	static int distance(int i, int j, int k) {
      int temp;
      if (j > i) {
        temp = i;
        i = j;
       	j = temp;
      }
      return Math.min(i - j, j + k - i);
    }
  
	public static void main(String[] args) {
      
    	Scanner sc = new Scanner(System.in);
      	int k = sc.nextInt();
      	int n = sc.nextInt();
      
        // 目的地点のリスト points を作成
     	List<Integer> points = new ArrayList<Integer>(n);
      	for (int i = 0; i <  n; i++) {
          points.add(sc.nextInt());
        }
      
      	// 各地点の距離の最大値を求める
      	int maxValue = 0;
      	int val;
      	
      	for (int i = 0; i < n; i++) {
        	for (int j = 0; j < i; j++) {
              val = distance(points.get(i), points.get(j), k);
              maxValue = val > maxValue ? val : maxValue; 
            }
        }
      System.out.println(maxValue);
    }
 }