import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int B = sc.nextInt();
		int N = sc.nextInt();
		int[] C = new int[N];
		for (int i = 0; i < C.length; i++) {
			C[i] = sc.nextInt();
		}
		sc.close();

		long min = Long.MAX_VALUE;
		for (int i = 0; i < C.length; i++) {
			long V = C[i];

			long sum = B;
			for (int j = 0; j < C.length; j++) {
				sum += C[j];
			}
			if (sum < N * V) {
				V = sum / N;
			}

			long stock = B;
			long ope = 0;
			for (int j = 0; j < C.length; j++) {
				// 取り上げ
				stock += Math.max(0, C[j] - V);
				ope += Math.max(0, C[j] - V);
			}
			for (int j = 0; j < C.length; j++) {
				// 配る
				stock -= Math.max(0, V - C[j]);
				ope += Math.max(0, V - C[j]);
			}
			min = Math.min(min, ope);

		}
		System.out.println(min);

	}

}