#include "boxes.h"
#include<bits/stdc++.h>
using namespace std;
// #define int long long
long long delivery(int n, int k, int l, int p[]) {
if (n <= k) {
long long ans = 0;
for (int i = 0; i < n; i++) ans = max(ans, 1LL * min(p[i], l - p[i]));
return 2LL * ans;
}
vector<long long> pre(n + 1, 0);
vector<long long> suf(n + 1, 0);
for (long long i = 0; i < n; i++) {
pre[i] = 2 * p[i] * 1LL;
if(i >= k){
pre[i] += pre[i - k];
}
}
for (long long i = n - 1; i >= 0; i--) {
suf[i] = 2 * (l - p[i]) * 1LL;
if (i < n - k) {
suf[i] += suf[i + k];
}
}
long long ans = 1LL * min(suf[0], pre[n - 1]);
for (long long i = 0; i < n - 1; i++) {
ans = min(ans, 1LL * (pre[i] + suf[i + 1]));
}
return ans;
}
