#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iterator>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
//#include <utility>
//#include <memory>
//#include <functional>
//#include <deque>
//#include <cctype>
//#include <ctime>
//#include <numeric>
//#include <list>
//#include <iomanip>

//#if __cplusplus >= 201103L
//#include <array>
//#include <tuple>
//#include <initializer_list>
//#include <forward_list>
//
//#define cauto const auto&
//#else

//#endif

using namespace std;


typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}


#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()
#define DEBUG
#ifdef DEBUG
#define dump(x)  cout << #x << " = " << (x) << endl;
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#else
#define dump(x) 
#define debug(x) 
#endif

#define MOD 1000000007LL
#define EPS 1e-8
static const int INF=1<<24;
vll v;

ll foo(ll a){
	ll ret=0;
	rep(i,v.size()){
		ret+=abs(v[i]-a);
	}
	return ret;
}
void mainmain(){
	ll b;
	ll n;
	cin>>b>>n;
	v=vll(n);
	rep(i,n) cin>>v[i];
	ll sum=0;
	rep(i,n) sum+=v[i];
	if(n==1){
		cout<<0<<endl;
		return;
	}
	sum+=b;
	sum/=n;
	ll l=0;
	ll r=sum;
	while(r-l>=10){
		ll t1=l+(r-l)/3;
		ll t2=l+(r-l)/3*2;
		ll tt1=foo(t1);
		ll tt2=foo(t2);
		if(tt2>tt1){
			r=t2;
		}
		else{
			l=t1;
		}
	}
	// cout<<l<<" "<<r<<endl;
	ll ans=LLONG_MAX;
	for(ll i=max(l-1000,0LL);i<min(r+1000,sum+1);i++) {
		// cout<<i<<" "<<foo(i)<<endl;
		ans=min(ans,foo(i));
	}
	cout<<ans<<endl;
}


main() {
    mainmain();
}