#include <bits/stdc++.h>
#include "boxes.h"
using namespace std;
const int maxn = 1e7+10;
typedef long long ll;
int p[maxn];
ll pref[maxn], suf[maxn];
long long delivery(int N, int K, int L, int positions[])
{
int n = N, k = K;
for (int i = 1; i <= n; i++)
p[i] = positions[i-1];
pref[1] = 2ll*p[1];
for (int i = 2; i <= n; i++)
pref[i] = 2ll*p[i] + pref[max(0, i-k)];
suf[n] = 2ll*(L-p[n]);
for (int i = n-1; i >= 1; i--)
suf[i] = 2ll*(L-p[i]) + suf[min(n+1, i+k)];
ll ans = min(pref[n], suf[1]);
if (k == n) ans = min(ans, 1ll*L);
for (int i = 1; i < n; i++)
ans = min(ans, pref[i]+suf[i+1]);
for (int i = 1; i <= n-k; i++)
ans = min(ans, pref[i] + 1ll*L + suf[i+k+1]);
return ans;
}
