#include "bits/stdc++.h"
using namespace std;
#define rt return
#define FOR(i,j,k) for(int i=j; i<(int)k;++i)
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    int N, M;
    while(cin >> N >> M){
        vi D(M);
        rep(i, M)cin >> D[i];
        sort(all(D));
        int ans = 1 << 30;
        for(int i = 0; i + N <= M; ++i){
            int mi = min(0,D[i]), ma = max(0,D[i+N-1]);
            mi = abs(mi);
            if(mi > ma)swap(mi, ma);
            smin(ans, mi * 2 + ma);
        }
        cout << ans << endl;
    }
}