#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <functional>
#include <set>
#include <sstream>
#include <map>
#include <queue>
#include <stack>

using namespace std;

const long long mod=1000000007; 

int main()
{

	int n,m;
	cin>>n>>m;
	
	vector<int> d;
	for(int i=0;i<m;i++){
		int dd;
		cin>>dd;
		if(dd==0) n--;
		else d.push_back(dd); 
	}
	sort(d.begin(),d.end());
	
	int res=99999999;
	for(int i=0;i+n-1<d.size();i++){
		int l=d[i],r=d[i+n-1];
		int len;
		if(0<=l) len=r;
		else if(r<=0) len=-l;
		else{
			len=min(2*r-l,-2*l+r);
		}
		
		res=min(res,len);
	}
	
	if(n==0) res=0;
	cout<<res<<endl;
	

	return 0;
}