#include<algorithm>
#include<complex>
#include<ctype.h>
#include<iomanip>
#include<iostream>
#include<fstream>
#include<map>
#include<math.h>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<stdio.h>
#include<string>
#include<string>
#include<vector>

using namespace std;
typedef long long ll;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

template < typename T >
void vprint(T &V){
	for(auto v : V){
    	cout << v << " ";
	}
	cout << endl;
}

ll B, N;
vector<ll> A;

// 何回操作が必要か
ll how_many(ll target){
    ll stock = B;
    ll scarcity = 0;
    for(ll a : A){
        if(a>target){
            ll diff = a - target;
            stock += diff;
        }
        else if(a<target){
            ll diff = target - a;
            scarcity += diff;
        }
    }

    if(stock>=scarcity){
        // 集めた分
        ll collect = stock - B;
        // 埋める分
        // scarcity
        return collect + scarcity;
    }else{
        // 達成不可能
        return inf;
    }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    cin >> B >> N;
    A.resize(N);

    FOR(i, 0, N){
        cin >> A.at(i);
    }
    sort(ALL(A));

    ll left = 0;
    ll right = *max_element(ALL(A));
    
    while(right-left>3){
        ll p0 = (2 * left + 1 * right) / 3;
        ll p1 = (1 * left + 2 * right) / 3;

        ll n0 = how_many(p0);
        ll n1 = how_many(p1);

        if(n0==inf){
            right = p0;
        }
        else if(n1==inf){
            right = p1;
        }
        else if(n0<n1){
            right = p1;
        }
        else{
            left = p0;
        }
    }

    ll num = inf;
    FOR(i, left, right+1){
        ll n = how_many(i);
        num = min(num, n);
    }
    p(num);
    
    return 0;
}