#include <bits/stdc++.h>
#define FOR(i, a, b) for(int i=(a); i<(b); i++)
#define REP(i, n) FOR(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define bit(x) (1L << (x))
using ll = long long;
using namespace std;

template<typename T>
vector<T> make_v(size_t a,T b){return vector<T>(a,b);}
 
template<typename... Ts>
auto make_v(size_t a,Ts... ts){
    return vector<decltype(make_v(ts...))>(a,make_v(ts...));
}

int main() {
    ll b, n; cin >> b >> n;
    ll sum = b;
    vector<ll> c(n);

    REP(i, n) {
        cin >> c[i];
        sum += c[i];
    }

    auto f = [&](ll x) {
        ll cost = 0;

        REP(i, n) {
            if (c[i] < x) {
                cost += x - c[i];
            } 

            if (c[i] > x) {
                cost += c[i] - x;
            }
        }

        return cost;
    };

    ll l = 0, r = sum / n + 1;
    REP(_, 10000) {
        ll t1 = (2 * l + r) / 3, t2 = (l + r * 2) / 3;

        if (f(t1) >= f(t2)) {
            l = t1;
        } else {
            r = t2;
        }
    }

    ll ans = 1e9;
    FOR(i, l, r + 1) ans = min(ans, f(i));

    cout << ans << endl;

    return 0;
}