#include "boxes.h"
#ifdef t9unkubj
#include"debug.cpp"
//#include"template_no_debug.h"
#else
#define dbg(...) 199958
#endif
#undef _GLIBCXX_DEBUG
#pragma GCC optimize("O3")
using namespace std;
#include<bits/stdc++.h>
using ll=long long;
using ull=unsigned long long;
template<class T>using vc=vector<T>;
template<class T>using vvc=vc<vc<T>>;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define REP(i,j,n) for(ll i=(j);i<(ll)(n);i++)
#define DREP(i,n,m) for(ll i=(n);i>=(m);i--)
#define drep(i,n) for(ll i=((n)-1);i>=0;i--)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
template<class T,class F>
bool chmin(T &x, F y){
if(x>y){
x=y;
return true;
}
return false;
}
template<class T, class F>
bool chmax(T &x, F y){
if(x<y){
x=y;
return true;
}
return false;
}
double pass_time=0;
ll solve(int n,int k,int l,vc<int>p){
vc<ll>L(n+1),R(n+1);
rep(i,n){
if(i+1-k>=0){
L[i+1]=L[i+1-k]+(p[i])*2;
}else{
L[i+1]=p[i]*2;
}
}
drep(i,n){
if(i+k<=n){
R[i]=R[i+k]+(l-p[i])*2;
}else{
R[i]=(l-p[i])*2;
}
}
dbg(L,R);
ll ans=min(L.back(),R[0]);
rep(i,n){
chmin(ans,(L[i]+R[i]));
}
rep(i,n-k+1){
chmin(ans,(L[i]+R[i+k]+l));
}
return ans;
}
long long delivery(int N, int K, int L, int p[]) {
vc<int>P(N);
rep(i,N)P[i]=p[i];
return solve(N,K,L,P);
}
namespace judge{
void run(){
int n,k,l;
cin>>n>>k>>l;
vc<int>p(n);
rep(i,n)cin>>p[i];
dbg(solve(n,k,l,p));
}
};
//int main(){judge::ch();}
//g++ graders/boxes.cpp -D t9unkubj
