#include<bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#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;
}

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

    // input
    ll N, M;
    cin >> N >> M;

    vector<ll> A; // 正の方向
    vector<ll> B; // 負の方向

    FOR(i, 0, M){
        ll x; cin >> x;

        if(x==0){
            N -= x;
            if(N<=0){
                p(0);
                return 0;
            }
        }

        if(x>0){
            A.push_back(x);
        }else{
            B.push_back(-x); // 正で入れる
        }
    }
    sort(ALL(A));
    sort(ALL(B));

    ll min_length = inf;
    
    // 片道で行ける場合
    if(A.size()>=N){
        chmin(min_length, A[N-1]);
    }
    if(B.size()>=N){
        chmin(min_length, B[N-1]);
    }

    if(A.size()==0 || B.size()==0){
        p(min_length);
        return 0;
    }

    // 折り返す
    // Aでi個取る場合
    FOR(i, 1, A.size()){
        ll path0 = A[i-1];
        
        // Bでj個取る
        ll j = N-i;
        ll path1;
        if(j==0){
            path1 = 0;
        }else{
            path1 = B[j-1];
        }

        ll length = min(2*path0 + path1, 2*path1 + path0);
        chmin(min_length, length);
    }

    p(min_length);

    return 0;
}