#include <bits/stdc++.h>
#define MAXN 1005
using namespace std;
inline int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
inline void print(int x){
	static int s[20],t=0;
	do s[++t]=x%10,x/=10;while(x);
	while(t) putchar(s[t--] + '0');
}

int n;int m,cnt=0;
int a[MAXN];
int dis[MAXN];

signed main(){
	n=read();m=read();
	vector<int> d(m);
	for(int i=0;i<m;i++){
		d[i]=read();
	}
    sort(d.begin(), d.end());
    int minn=1e9;
    for(int i=0;i<m;i++){
        int st=i+n-1;
        if(st>=m) break;
        for(int j=st;j<m;j++){
            int L=d[i];
            int R=d[j];
            int cur=(R-L)+min(abs(L),abs(R));
            minn=min(minn,cur);
        }
    }
    cout<<minn;
	return 0;
}