#include "boxes.h"

#include <bits/stdc++.h>

long long delivery(int n, int k, int L, int p[]) {
    int it = std::lower_bound(p, p + n, (L + 1) / 2) - p;
    int64_t ans1 = 0;
    for (int i = 0; i < it; i += k) {
        int nx = std::min(it - 1, i + k - 1);
        ans1 += 2 * p[nx];
    }
    for (int i = n - 1; i >= it; i -= k) {
        int nx = std::max(it, i - k + 1);
        ans1 += 2 * (L - p[nx]);
    }

    return ans1;
}