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

#define int long long
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>inline void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>inline void chmax(T &t,U f){if(t<f)t=f;}

int N,M;
signed main(){
    cin>>N>>M;
    vint A,B;
    rep(i,M){
        int d;cin>>d;
        if(d<0)A.pb(-d);
        else if(d==0)N--;
        else B.pb(d);
    }

    if(N<=0){
        cout<<0<<endl;
        return 0;
    }

    sort(all(A));sort(all(B));
    int mi=1001001001;

    rep(hoge,2){
        if(A.size()>=N)chmin(mi,A[N-1]);
        rep(i,A.size()){
            if(i>=N-1)break;
            int t=N-i-1;
            if(B.size()>=t)chmin(mi,A[i]*2+B[t-1]);
        }
        swap(A,B);
    }
    cout<<mi<<endl;
    return 0;
}