#include "boxes.h"
#include <bits/stdc++.h>
using namespace std;
#define name "boxes"
#define MAXN 10000007
#define pb push_back
#define pf push_front
#define ll long long
#define ii pair<int, int>
#define fs first
#define sc second
#define ill pair<int, ll>
#define lli pair<ll, int>
#define llll pair<ll, ll>
#define all(v) v.begin(),v.end()
#define uni(v) v.erase(unique(all(v)),v.end())
#define bit(n,i) (((n)>>(i))&1)
#define FOR(i,a,b) for (int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for (int i=(a),_b=(b); i>=_b; i--)
#define MASK(i) (1LL<<(i))
const int INF=1e9;
const int MOD=1e9+7;
void add(int &u, int v){
u+=v;
if (u>=MOD) u-=MOD;
}
void sub(int &u, int v){
u-=v;
if (u<0) u+=MOD;
}
void minimize(ll &u, ll v){
u=min(u,v);
}
void maximize(int &u, int v){
u=max(u,v);
}
long long Rand(long long l, long long r){
ll tmp=0;
FOR(i,1,4) tmp=((tmp<<15)^(((1<<15)-1)&rand()));
return l+tmp%(r-l+1);
}
ll dp[MAXN],dpd[MAXN];
ll delivery(int n, int k, int L, int positions[]){
FOR(i,0,n-1){
dp[i]=(i>=k?dp[i-k]:0LL)+1LL*2*positions[i];
}
FORD(i,n-1,0){
dpd[i]=(i+k<=n-1?dpd[i+k]:0LL)+1LL*2*(L-positions[i]);
}
ll res=1e18;
FOR(i,0,n-1){
ll x=(i==0?0LL:dp[i-1]);
ll y=(i+k-1==n-1?0LL:dpd[i+k]);
minimize(res,x+y+1LL*L);
x=dp[i];
y=(i==n-1?0LL:dpd[i+1]);
minimize(res,x+y);
}
return res;
}
