import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		long B = scan.nextLong();
		int N = scan.nextInt();
		long[] C = new long[N];
		long sum = B;
		for(int i = 0; i < N; i++) {
			C[i] = scan.nextLong();
			sum += C[i];
		}
		scan.close();
		if(N == 1) {
			System.out.println("0");
			System.exit(0);
		}
		long r = sum / N;
		long l = 0;

		long min = Long.MAX_VALUE;
		while(r - l > 3) {
			// 幅 len = (r - l) / 3
			// x1 = l + len = (2l + r) / 3
			// x2 = x1 + len = (l + 2r) / 3
			long x1 = (l * 2 + r) / 3;
			long x2 = (l + r * 2) / 3;
			long t1 = 0;
			long t2 = 0;
			for(int i = 0; i < N; i++) {
				t1 += Math.abs(x1 - C[i]);
				t2 += Math.abs(x2 - C[i]);
			}
			if(t1 > t2) {
				l = x1;
			}else {
				r = x2;
			}
		}
		for(long i = l; i <= r; i++) {
			long t = 0;
			for(int j = 0; j < N; j++) {
				t += Math.abs(i - C[j]);
			}
			min = Math.min(min, t);
		}
		System.out.println(min);
	}
}