#include "boxes.h"
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vii;
typedef vector<ll> vll;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<vii> vvii;
typedef vector<vll> vvll;
typedef vector<vpii> vvpii;
typedef vector<vpll> vvpll;
#define ffor(i, a, b) for (ll i = (a); i < (ll)(b); i++)
#define fford(i, a, b) for (ll i = (a); i > (ll)(b); i--)
#define rep(i, n) ffor(i, 0, n)
#define forin(x, a) for (auto &x: a)
#define all(a) a.begin(), a.end()
long long delivery(int N, int K, int L, int p[]) {
vll left = {0}, right = {0};
rep(i, N) {
if (i % K) {
left.emplace_back(left.back() + 2 * (p[i] - p[i - 1]));
} else {
left.emplace_back(left.back() + 2 * p[i]);
}
}
rep(i, N) {
if (i % K) {
right.emplace_back(right.back() + 2 * (p[N - i] - p[N - i - 1]));
} else {
right.emplace_back(right.back() + 2 * (L - p[N - i - 1]));
}
}
ll res = left[N];
rep(i, N) {
res = min(res, left[i] + right[N - i]);
}
return res;
}
