#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <cmath>

using namespace std;

vector<int> c;

long long calc(long long a) {
	long long ret = 0;
	for (auto x : c) {
		ret += abs(x - a);
	}
	return ret;
}

int main() {
	int b, n;
	cin >> b >> n;
	c.assign(n, 0);
	long long total = b;
	for (int i = 0; i < n; i++) {
		cin >> c[i];
		total += c[i];
	}

	long long lower = 0;
	long long upper = floor(1.0 * total / n);
	long long mid1, mid2;
	while (upper - lower > 2) {
		mid1 = lower + (upper - lower) / 3;
		mid2 = lower + (upper - lower) / 3 * 2;

	// printf("%lld %lld %lld %lld\n", lower, mid1, mid2, upper);

		long long move1 = calc(mid1);
		long long move2 = calc(mid2);

		if (move1 < move2) {
			upper = mid2;
		} else {
			lower = mid1;
		}
	}

	long long ans = 1e18;
	for (long long i = lower; i <= upper; i++) {
		ans = min(ans, calc(i));
	}

	cout << ans << endl;
	return 0;
}