#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(int argc, char *argv[])
{
  int n, m;
  cin >> n >> m;
  vector<int> xs(m);
  for (int i = 0; i < m; i++) cin >> xs[i];

  sort(xs.begin(), xs.end());
  int ret = 1<<30;
  for (int i = 0; i + n <= m; i++) {
    int tmp = (xs[i+n-1] - xs[i]) + min(abs(xs[i]), abs(xs[i+n-1]));
    ret = min(ret, tmp);
  }

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