#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>
#include <random>

#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define RREP(i, a) for(int (i) = (a)-1; (i) >= 0; (i)--)
#define FORR(i, a, b) for(int (i) = (a)-1; (i) >= (b); (i)--)
#define PI acos(-1.0)
#define DEBUG(C) cerr << C << endl;
#define VI vector <int>
#define VII vector <VI>
#define VL vector <LL>
#define VLL vector <VL>
#define VD vector <double>
#define VDD vector <VD>
#define PII pair <int, int>
#define PDD pair <double, double>
#define PLL pair <LL, LL>
#define VPII vector <PII>
#define ALL(a) (a).begin(), (a).end()
#define SORT(a) sort(ALL(a))
#define REVERSE(a) reverse(ALL(a))
#define MP make_pair
#define EB emplace_back
#define FORE(a, b) for (auto &&a : b)
#define FIND(s, n) (s.find(n) != s.end())

using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;

int main(void) {
    int N, M;
    cin >> N >> M;
    VI D(M);
    int lcnt = 0, rcnt = 0;
    int zp = -1;
    REP(i, M) cin >> D[i];
    SORT(D);
    REP(i, M) {
        if (D[i] < 0) lcnt++;
        else if (D[i] > 0) rcnt++;
        if (D[i] >= 0 && zp == -1) {
            zp = i;
        }
    }
    if (D[zp] == 0) {
        N--;
        D.erase(D.begin() + zp);
    }
    if (N == 0) {
        cout << 0 << endl;
        return 0;
    }
    int ans = INF;
    if (lcnt >= N) {
        ans = min(ans, -D[lcnt - N]);
    }
    if (rcnt >= N) {
        ans = min(ans, D[lcnt + N -1]);
    }
    REP(i, D.size() - N) {
        if (!(D[i] <= 0 && 0 <= D[i + N - 1])) {
            continue;
        }
        int buf = D[i + N - 1] - D[i];
        buf += min(abs(D[i + N - 1]), abs(D[i]));
        ans = min(ans, buf);
    }
    cout << ans << endl;
    return 0;
}