#include <bits/stdc++.h>
using namespace std;
const int N = 1e7 + 7;
vector<long long> v1, v2;
vector<long long> v3, v4;
void output(vector<long long> v){
for(long long &x: v){
cout << x << " ";
}
cout << endl;
}
long long delivery(int n, int k, int l, int *positions){
sort(positions, positions + n);
int idx = 0;
for(; idx < n && positions[idx] <= l / 2; idx++){
v1.push_back(positions[idx]);
}
for(; idx < n; idx++){
v2.push_back(l - positions[idx]);
}
if(!v2.empty()){
reverse(v2.begin(), v2.end());
}
//output(v1);
//output(v2);
long long ans = 0;
for(int i = -1; true;){
if(i + k >= (int)v1.size()){
for(++i; i < (int)v1.size(); ++i){
v3.push_back(v1[i]);
}
break;
}
i += k;
ans += (long long)v1[i] * 2ll;
}
for(int i = -1; true;){
if(i + k >= (int)v2.size()){
for(++i; i < (int)v2.size(); ++i){
v4.push_back(v2[i]);
}
break;
}
i += k;
ans += (long long)v2[i] * 2ll;
}
//output(v3);
//output(v4);
if(v3.empty() || v4.empty()){
if(!v3.empty()){
ans += v3.back() * 2ll;
}
if(!v4.empty()){
ans += v4.back() * 2ll;
}
return ans;
}
return ans;
}
/*int positions[N], n, k, l;
int main(){
cin >> n >> k >> l;
for(int i = 0; i < n; i++){
cin >> positions[i];
}
cout << delivery(n, k, l, positions) << "\n";
return 0;
}*/
/*
3 2 8
1 2 5
*/
