#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vi;
typedef pair<ll,ll> ii;
typedef vector<ii> vii;
typedef long double lld;
#define rep(i,a,b) for(ll i = a; i < b; i++)
#define per(i,a,b) for(ll i = a; i >= b; i--)
#define all(x) x.begin(),x.end()
#define sz(x) (ll)(x).size()
#define trav(a,x) for(auto a : x)
#define inf 1000000000000000000
ll n,myL,k;
vi a;
long long find(ll h, ll v){
if (h+v > n) return inf;
ll l = n-h-v;
ll res = ((l+k-1)/k)*myL;
ll cur = h-1;
while(cur >= 0){
res += a[cur]*2;
cur -= k;
}
cur = n-v;
while (cur < n){
res += (myL-a[cur])*2;
cur += k;
}
return res;
}
long long delivery(int N, int K, int L, int p[]) {
ll best = inf; n = N, myL = L, k = K;
rep(i,0,N) {
if (p[i] == 0) n--;
else a.push_back(p[i]);
}
rep(h,0,n+1) rep(v,0,n+1) best = min(best, find(h,v));
return best;
}
