#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 tv = c[0], fv = sum / n + 1;
    while (fv - tv >= 3) {
        long long mid1 = (tv * 2 + fv) / 3;
        long long mid2 = (tv + fv * 2) / 3;
        if (search(mid1) > search(mid2)) tv = mid1; //左側が高い
        else fv = mid2; //右側が高い
    }
	cout << search((tv + fv) / 2) << endl;
	return (0);
}