#include <iostream>
#include <vector>
#include <iomanip>
#include <cmath>
using namespace std;
using ll = long long;

ll n, m, d[1010], e[1010];

int main()
{
  cin >> n >> m;
  for (int i = 0; i < m; ++i)
    cin >> d[i];

  ll ans = 1 << 30;
  for (int i = 0; i < m - n + 1; ++i)
  {
    ans = min(ans, min(abs(d[i + n - 1]), abs(d[i])) + d[i + n - 1] - d[i]);
  }
  cout << ans << endl;
  return 0;
}