#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
const ll INF = 1e18;

ll b;
vector<ll> c;
int n;

ll search(ll m){
    ll cnt = 0;
    rep(i, n){
        cnt += abs(m - c[i]);
    }
    return cnt;
}

int main(void){
    cin >> b >> n;
    ll sum = b;
    rep(i, n){
        ll t; cin >> t;
        c.push_back(t);
        sum += t;
    }

    if(n == 1){
        printf("0\n");
        return 0;
    }

    sort(c.begin(), c.end());
    //下凸関数を三分探索
    ll l = 0;
    ll r = ( int ) 1e9 + 1;
    while(r - l > 3){
        ll m1 = (l * 2 + r) / 3;
        ll m2 = (l + r * 2) / 3;

        if(search(m1) > search(m2)){//左側が高い
            l = m1;
        }else{//右側が高い
            r = m2;
        }
    }

    ll ans = INF;
    for (int i = l; i < r; ++i){
        ans = min(ans, search(i));
    }
    printf("%lld\n", ans);
    return 0;
}