#include <bits/stdc++.h>
using namespace std;

vector<long long> c;
int n;

long long search(long long m) {
    long long cnt = 0;
    for (int i = 0; i < n; i++) cnt += abs(m - c[i]);
    return (cnt);
}

int main() {

	long long b;
    cin >> b >> n;
	c.resize(n);
    for (int i = 0; i < n; i++) cin >> c[i];

	if (n == 1) {
		cout << 0 << endl;
        return (0);
    }
    long long sum = b;
    for (int i = 0; i < n; i++) sum += c[i];
    sort(c.begin(), c.end());
    long long l = c[0], r = sum / n + 1;
    while (r - l > 3) {
        long long mid1 = (l * 2 + r) / 3;
        long long mid2 = (l + r * 2) / 3;
        if (search(mid1) > search(mid2)) l = mid1;
        else r = mid2;
    }
    long long ans = 1e18;
    for (int i = l; i < r; ++i) ans = min(ans, search(i));
	cout << ans << endl;
	return (0);
}