#include "boxes.h"
#include <bits/stdc++.h>
using namespace std ;
const int N = 1e7 + 4 ;
template <class T>
bool chmin( T &x , const T &y ){
bool f = 0 ;
if ( x > y ) x = y , f = 1 ;
return f ;
}
long long dpl[N] , dpr[N] ;
long long delivery(int n, int k, int l, int a[]) {
for ( int i = 1 ; i <= n ; i ++ ) dpl[i] = dpl[max(i-k,0)] + min(l,2*a[i-1]) ;
for ( int i = n ; i > 0 ; i -- ) dpr[i] = dpr[min(i+k,n+1)] + min(l,2*(l-a[i-1])) ;
long long ans = min(dpr[1],dpl[n]) ;
for ( int i = 1 ; i < n ; i ++ ) chmin ( ans , dpl[i]+dpr[i+1] ) ;
return ans ;
}
/*
int a[N] ;
signed main(){
int n , k , l ; cin >> n >> k >> l ;
for ( int i = 0 ; i < n ; i ++ ) cin >> a[i] ;
cout << delivery( n , k , l , a ) ;
}
//*/
