import java.util.*;

public class Exercise88{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    long h = sc.nextInt();
    int n = sc.nextInt();
    long[] box = new long[n];
    long sum = 0;
    long ave = 0;

    for(int i = 0; i < n; i++){
      box[i] = sc.nextInt();
      sum += box[i];
    }
    sum += h;
    Arrays.sort(box);
    ave = sum / (long)n;
    ave = Math.min(sum / n, box[n / 2]);
    long answer = 0;
    for(int i = 0; i < box.length; i++){
      long x = box[i] - ave;
      if(x == 0){
        continue;
      }else if(x < 0){
      answer += x * -1;
      }else{
      answer += x;
      }
    }
    System.out.println(answer);
  }
}