#include <algorithm>
#include <iostream>
using namespace std;

int main() {
	int norma, m;
	cin >> norma >> m;
	int dust[m];
	for (int i = 0; i < m; i++) {
		cin >> dust[i];
	}
	sort(dust, dust+m);
	int ans = 0x7FFF;
	for (int i = 0; i <= m - norma; i++) {
		if (dust[i] * dust[i+norma-1] >= 0) {
			ans = min(ans, max(abs(dust[i]), abs(dust[i+norma-1])));
		} else {
			ans = min(ans, abs(dust[i] - dust[i+norma-1]) + min(abs(dust[i]), abs(dust[i+norma-1])));
		}
	}
	cout << ans << endl;
	return 0;
}