#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<ll>> vvll;
const ll inf = 1e16;
const ll md = 1000000007;

int main() {
  ll b,n;
  vll cc;
  cin>>b>>n;
  ll s=0LL;
  rep(_,n){
    ll c;
    cin>>c;
    cc.push_back(c);
    s+=c;
  }
  sort(cc.begin(),cc.end());
  ll k=cc[(n-1)/2];
  while (k*n>s+b) k--;
  ll ans=0;
  for(ll c:cc) ans+=abs(k-c);
  cout<<ans<<endl;
  return 0;
}