#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

int main() {
    int N, M;
    cin >> N >> M;
    vector<int> d(M);
    for (int i = 0; i < M; ++i) {
        cin >> d[i];
    }
    sort(d.begin(), d.end());
    
    int min_distance = 1e9;
    for (int i = 0; i < M; ++i) {
        int j_start = i + N - 1;
        if (j_start >= M) break;
        for (int j = j_start; j < M; ++j) {
            int L = d[i];
            int R = d[j];
            int current = (R - L) + min(abs(L), abs(R));
            if (current < min_distance) {
                min_distance = current;
            }
        }
    }
    cout << min_distance << endl;
    return 0;
}