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

int main() {
    int n, m;
    cin >> n >> m;
    // 正の近傍
    priority_queue<int, vector<int>, greater<int>> pos_neighbor;
    // 負の近傍
    priority_queue<int> neg_neighbor;
    for (int i = 0; i < m; i++) {
        int d;
        cin >> d;
        if (d >= 0) pos_neighbor.push(d);
        else neg_neighbor.push(d);
    }

    int pos_end = 0, neg_end = 0, num = 0;
    while (num < n) {
        if (neg_neighbor.empty()) {
            pos_end = pos_neighbor.top(); pos_neighbor.pop();
        } else if (pos_neighbor.empty()) {
            neg_end = neg_neighbor.top(); neg_neighbor.pop();
        } else if (abs(neg_neighbor.top() - neg_end) < abs(pos_neighbor.top() - pos_end)) {
            neg_end = neg_neighbor.top(); neg_neighbor.pop();
        } else {
            pos_end = pos_neighbor.top(); pos_neighbor.pop();
        }
        num++;
    }
    int ans = min(abs(neg_end), abs(pos_end)) + abs(neg_end) + abs(pos_end);
    cout << ans << endl;

    return 0;
}