#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define p(s) cout<<(s)<<endl
#define REP(i,n,N) for(int i=n;i<N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=n;i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define F first
#define S second
typedef long long int ll;
using namespace std;
const int inf=1e9+7;

int N, M;
int D[1010];
int ans;
int main(){
    cin>>N>>M;
    REP(i,0,M) {
        cin >> D[i];
    }
    sort(D, D+M);
    ans = inf;
    REP(l,0,M-N+1){
        if(D[l]*D[l+N-1]<0){
            ans = min(ans, max(abs(D[l]),abs(D[l+N-1]))+min(abs(D[l]),abs(D[l+N-1]))*2);
        }else{
            ans = min(ans, max(abs(D[l]),abs(D[l+N-1])));
        }
    }
    p(ans);
    return 0;
}