#include "boxes.h"
#include <bits/stdc++.h>
#define MAXN 1000006
#define INF (1LL << 62LL)
using namespace std;
typedef long long ll;
int N, K, L, lbound;
ll DP[MAXN], pre[MAXN], cost;
vector < int > P;
ll delivery ( int _n, int _k, int _l, int _p[] )
{
N = _n, K = _k, L = _l;
P.push_back ( 0 );
for ( int i = 0; i < N; i++ )
P.push_back ( _p[i] );
P.push_back ( L );
for ( int i = 1; i <= N + 1; i++ )
{
pre[i] = pre[i - 1] + (P[i] - P[i - 1]);
if ( 2 * P[i] < L )
lbound = i;
}
for ( int i = N; i >= 1; i-- )
{
DP[i] = INF;
for ( int k = 1; k <= K; k++ )
{
if ( i + k <= N + 1 )
{
if ( i + k - 1 <= lbound )
cost = 2 * pre[i + k - 1];
else
cost = min ( (ll)L, 2 * (pre[N + 1] - pre[i]) );
DP[i] = min ( DP[i], cost + DP[i + k] );
}
}
}
return DP[1];
}
