#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N,M,D[10101];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>M;
	FOR(i,M) cin>>D[i];
	sort(D,D+M);
	int mi=1<<30;
	for(x=0;x<M;x++) {
		y=x+(N-1);
		if(y>=M) continue;
		if(D[x]>=0) mi=min(mi,D[y]);
		if(D[y]<=0) mi=min(mi,-D[x]);
		if(D[x]<=0 && D[y]>=0) {
			mi=min(mi,-D[x]+2*D[y]);
			mi=min(mi,-2*D[x]+D[y]);
		}
	}
	cout<<mi<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n';
	FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	solve(); return 0;
}