#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdlib>

#define rep(i,a,b) for(int i=a;i<b;i++)

using namespace std;

int main()
{
	int i, j, n, m, f=0, tmp, max= 1 << 30;
	vector<int> road;
	cin >> n >> m;
	rep(i, 0, m) {
		cin >> tmp;
		road.push_back(tmp);
		if (tmp == 0) f = 1;
	}
	if (!f) {
		road.push_back(0);
		n++;
		m++;
	}
	sort(road.begin(), road.end());

	int start;
	rep(i, 0, m) {
		if (road[i] == 0) start = i;
	}

	int sum = 0, left, right, lm;
	if (start - (n-1) > 0) {
		lm = start - (n-1);
	}
	else {
		lm = 0;
	}
	for (i = lm; i <= start && i + n-1 < road.size(); i++) {
		left = road[i];
		right = road[i + n-1];
		if (left >= 0) {
			sum = right;
		}
		else if (right <= 0) {
			sum = abs(left);
		}
		else {
			abs(left) < abs(right) ? sum = abs(left) * 2 + right : sum = abs(left) + right * 2;
		}
		if (sum < max) {
			max = sum;
		}
	}

	cout << max << endl;

	return 0;
}