#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000


int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int N, M;
	cin >> N >> M;
	int D[1010];
	rep(i, M) cin >> D[i];
	int ans = INF;
	rep(i, M - N + 1) {
		int L = D[i], R = D[i + N - 1];
		int cost;
		if (L * R < 0) {
			cost = min(-L + R * 2, -L * 2 + R);
		}
		else {
			cost = max(abs(L), abs(R));
		}
		//cout << cost << endl;
		ans = min(ans, cost);
	}
	cout << ans << endl;

    return 0;
}