#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;

    int left = it / k * k;
    int right = n - (n - it) / k * k;

    int64_t ans = 0;
    for (int i = 0; i < left; i += k) {
        ans += 2 * p[i + k - 1];
    }
    for (int i = n - 1; i >= right; i -= k) {
        ans += 2 * (L - p[i - k + 1]);
    }
    // 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 ans;
}