#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
typedef long long ll;
const ll INF = (ll)1e12;
int b, n;
vector<ll> c;

ll check(ll t) {
	ll sum = b;
	ll cost = 0;
	for(int i = 0; i < n; i++) {
		if(c[i] > t) {
			sum += c[i] - t;
			cost += c[i] - t;
		}
		else {
			sum -= t - c[i];
			cost += t - c[i];
			if(sum < 0) {
				return INF;
			}
		}
	}
	return cost;
}

int main() {
	cin >> b >> n;
	for(int i = 0; i < n; i++) {
		ll cc;
		cin >> cc;
		c.push_back(cc);
	}
	sort(c.begin(), c.end());
	reverse(c.begin(), c.end());
	ll l1 = 0, l2 = l1, r1 = (ll)1e9 + 3, r2 = r1;
	while(r1 - l1 > 2) {
		l2 = l1 + (r1 - l1) / 3, r2 = l1 + (r1 - l1) * 2 / 3;
		ll lc = check(l2), rc = check(r2);
		if(lc <= rc) {
			r1 = r2;
		}
		else {
			l1 = l2;
		}
	}
	ll ans = check(l1);
	ans = min(ans, check(l2));
	ans = min(ans, check(r1));
	ans = min(ans, check(r2));
	cout << ans << endl;
}