#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using db = double;
using str = string; // yay python!
using ii = pair<int,int>;
using pl = pair<ll,ll>;
using pd = pair<db,db>;
using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vii = vector<ii>;
using vpl = vector<pl>;
using vpd = vector<pd>;
#define tcT template<class T
#define tcTU tcT, class U
tcT> using V = vector<T>;
tcT, size_t SZ> using AR = array<T,SZ>;
tcT> using PR = pair<T,T>;
// pairs
#define mp make_pair
#define f first
#define s second
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
#define len(x) int((x).size())
#define bg(x) begin(x)
#define all(x) bg(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pb push_back
#define eb emplace_back
#define pf push_front
const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5;
const ll INF = 1e18; // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!
/*
#include <stdio.h>
#include <stdlib.h>
static char _buffer[1024];
static int _currentChar = 0;
static int _charsNumber = 0;
static FILE *_inputFile, *_outputFile;
static inline int _read() {
if (_charsNumber < 0) {
exit(1);
}
if (!_charsNumber || _currentChar == _charsNumber) {
_charsNumber = (int)fread(_buffer, sizeof(_buffer[0]), sizeof(_buffer), _inputFile);
_currentChar = 0;
}
if (_charsNumber <= 0) {
return -1;
}
return _buffer[_currentChar++];
}
static inline int _readInt() {
int c, x, s;
c = _read();
while (c <= 32) c = _read();
x = 0;
s = 1;
if (c == '-') {
s = -1;
c = _read();
}
while (c > 32) {
x *= 10;
x += c - '0';
c = _read();
}
if (s < 0) x = -x;
return x;
}
*/
#include "boxes.h"
long long delivery(int N, int K, int L, int p[]) {
vl left(N+1,INF),right(N+1,INF);
left[0] = 0; right[0] = 0;
for(int i=0; i<=N; i+=K){
if (i!=0){
left[i] = left[i-K] + 2*p[i-1];
right[i] = right[i-K] + 2*(L-p[N-i]);}
for(int j=i+1; j<min(i+K,N+1);++j){
left[j] = left[i] + 2*p[j-1];
right[j] = right[i] + 2*(L-p[N-j]);
}
}
ll ans = INF;
F0R(i, N+1) ans = min(ans, left[i]+right[N-i]);
F0R(i, N+1-K) ans = min(ans, left[i]+L+right[N-K-i]);
return ans;
}
/*
int main() {
_inputFile = fopen("boxes.in", "rb");
_outputFile = fopen("boxes.out", "w");
int N, K, L, i;
N = _readInt();
K = _readInt();
L = _readInt();
int *p = (int*)malloc(sizeof(int) * (unsigned int)N);
for (i = 0; i < N; i++) {
p[i] = _readInt();
}
fprintf(_outputFile, "%lld\n", delivery(N, K, L, p));
return 0;
}*/
