#include <bits/stdc++.h>
using namespace std;

signed main(){
  int N, M; cin >> N >> M;
  vector< int > D( M );
  for( int i = 0; i < M; ++i )
    cin >> D[ i ];
  sort( D.begin(), D.end() );
  int ans = 0x3f3f3f3f;
  for( int i = N - 1; i < M; ++i ){
    if( D[ i - ( N - 1 ) ] * D[ i ] < 0 )
      ans = min( ans, 2 * min( -D[ i - ( N - 1 ) ], D[ i ] ) + max( -D[ i - ( N - 1 ) ], D[ i ] ) );
    else
      ans = min( ans, max( abs( D[ i ] ), abs( D[ i - ( N - 1 ) ] ) ) );
  }
  cout << ans << endl;
  return 0;
}