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

template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
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=1e9;
  for(Int i=n-1;i<m;i++){
    Int j=i-(n-1);
    if(d[i]*d[j]>=0) chmin(ans,max(abs(d[i]),abs(d[j])));
    else chmin(ans,abs(d[i])+abs(d[j])+min(abs(d[i]),abs(d[j])));    
  }
  cout<<ans<<endl;
  return 0;
}