#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>
#include <cstring>
#include <random>
#include <functional>
#include <numeric>
#include <bitset>
#include <fstream>

using namespace std;

struct before_main{before_main(){cin.tie(0); ios::sync_with_stdio(false);}} before_main;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)
#define all(c) (c).begin(), (c).end()
#define zero(a) memset(a, 0, sizeof a)
#define minus(a) memset(a, -1, sizeof a)
template<class T1, class T2> inline bool minimize(T1 &a, T2 b) { return b < a && (a = b, 1); }
template<class T1, class T2> inline bool maximize(T1 &a, T2 b) { return a < b && (a = b, 1); }

typedef long long ll;

int main() {


  int N, M; cin >> N >> M;
  vector<int> D(M);
  bool f = 1;
  rep(i, M) {
    cin >> D[i];
    if(D[i] == 0 || (i && D[i] * D[i-1] >= 0)) {}
    else f = 0;
  }

  sort(all(D));

  ll ans = 1e10;

  if(f) {
    if(D[0] < 0 || (D[0] == 0 && N > 1 && D[1] < 0)) {
      ans = abs(D[M-1-N-1]);
    } else {
      ans = D[N-1];
    }
  }
  else {
    D.push_back(0); M++;
    sort(all(D));
    int zr = find(all(D), 0) - D.begin();
    if(zr + 1 < M && D[zr + 1] == 0) zr ++;
    if(zr >= N) {
      minimize(ans, abs(D[zr - N]));
    }
    if(zr - 1 >= 0 && D[zr - 1] == 0) zr --;
    if(zr + N <= M) {
      minimize(ans, abs(D[zr + N]));
    }
    rep(l, zr) REP(r, zr + 1, M) {
      minimize(ans, min(abs(D[l]) + abs(D[l] - D[r]), abs(D[r]) + abs(D[l] - D[r])));
    }
  }

  cout << ans << endl;
  
  return 0;
}