#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    int b, n;
    cin >> b >> n;
    vector<llong> c(n);
    rep(i, n) cin >> c[i];

    llong summary = accumulate(c.begin(), c.end(), 0);
    llong avgval = (int)round((double)summary / n);
    if((summary + b) / n < avgval) avgval--;
    llong result = 0;
    rep(i, n) result += abs(avgval - c[i]);

    cout << result << "\n";
}