#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n, m;
  cin >> n >> m;
  vector<int> D(m);
  REP (i, m) cin >> D[i];

  sort(D.begin(), D.end());

  int ret = 1e8;
  for (int i = 0; i + n - 1 < m; i++) {
    int j = i + n - 1;
    if (D[i] * D[j] >= 0) {
      ret = min(ret, max(abs(D[i]), abs(D[j])));
    } else {
      ret = min(ret, 2 * abs(D[i]) + abs(D[j]));
      ret = min(ret, abs(D[i]) + 2 * abs(D[j]));
    }
  }

  cout << ret << endl;
  
  return 0;
}