#include"boxes.h"
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
typedef long long ll;
#define chmin(a,b) a=min(a,b)
#define chmax(a,b) a=max(a,b)
#define rep(i,n) for(int i=0;i<n;i++)
#define mod 1000000007
#define mad(a,b) a=(a+b)%mod
ll delivery(int N,int K,int L,int P[]){
ll ans=1e17;
for(int i=0;i+K-1<N;i++){
ll res=L;
for(int j=i-1;j>=0;j-=K)res+=P[j]*2;
for(int j=i+K;j<N;j+=K)res+=(L-P[j])*2;
chmin(ans,res);
}
for(int i=0;i<=N;i++){
ll res=0;
for(int j=i-1;j>=0;j-=K)res+=P[j]*2;
for(int j=i;j<N;j+=K)res+=(L-P[j])*2;
chmin(ans,res);
}
return ans;
}/*
int main(){
int n,k,l,p[110];
cin>>n>>k>>l;
rep(i,n){
cin>>p[i];
}
cout<<delivery(n,k,l,p)<<endl;
}*/
