#include <iostream>
#include <queue>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <limits>
#include <cassert>
#include <fstream>
#include <cstring>
#include <bitset>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdio>
#include <ciso646>
#include <array>

using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

#define inf 0x3f3f3f3f
#define CLEAR(a) a = decltype(a)()
#define MP make_pair
#define ALL(a) (a).begin(),(a).end()
#define pii pair<int ,int>
#define pcc pair<char,char>
#define pic pair<int,char>
#define pci pair<char,int>
#define VS vector<string>
#define VI vector<int>
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define pi 2*acos(0.0)
#define INFILE() freopen("in.txt","r",stdin)
#define OUTFILE() freopen("out.txt","w",stdout)
#define ll long long
#define ull unsigned long long
#define eps 1e-14

int main(void) {
	int N, M; cin >> N >> M;
	vector<int> D(M); for (auto &a : D) cin >> a;

	sort(ALL(D));

	int mi = inf;

	for (int i = 0; i + N - 1 < D.size(); ++i) {
		int left = i;
		int right = i + N - 1;
		if (D[right] < 0) mi = min(-D[left], mi);
		else if (D[left] > 0) {
			mi = min(D[right], mi);
			break;
		}
		else {
			mi = min({ mi, -D[left] * 2 + D[right], -D[left] + 2 * D[right] });
		}
	}

	cout << mi << endl;

	return 0;
}