#include "boxes.h"
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define OVL(v,s) for(auto x:v) cout<<x<<s;cout<<endl;
#define all(v) v.begin(),v.end()
#define F first
#define S second
#define pb push_back
void dbg_out() { cout << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__);
#define endl "\n"
#define mod 1000000007
const ll INF=1e18;
long long delivery(int N, int K, int L, int p[]) {
vector<int> v;
v.push_back(0);
for(int i=0;i<N;i++) v.pb(p[i]);
sort(all(v));
v.push_back(0);
auto diff = [&](int a,int b){
//a is smaller than b
return min(b-a,L-b+a);
};
if(K==1){
// dbg;
ll ans=0;
// OVL(v," ")
for(auto x:v) ans+=2*diff(0,x);
// dbg(ans);
return ans;
}
else{
ll ans=0;
int kk=K;
for(int i=0;i+1<v.size();i++){
ans+=diff(min(v[i],v[i+1]),max(v[i],v[i+1]));
kk--;
if(kk==0){
ans+=diff(min(v[i],0),max(v[i+1],0));
kk=K;
v[i+1]=0;
}
}
return ans;
}
// return ans;
//{0,1,4,6,7,0}
//diff between going from i to i+1 in the same direction, or
}
#ifdef IOI
static char _buffer[1024];
static int _currentChar = 0;
static int _charsNumber = 0;
static FILE *_inputFile, *_outputFile;
static inline int _read() {
if (_charsNumber < 0) {
exit(1);
}
if (!_charsNumber || _currentChar == _charsNumber) {
_charsNumber = (int)fread(_buffer, sizeof(_buffer[0]), sizeof(_buffer), _inputFile);
_currentChar = 0;
}
if (_charsNumber <= 0) {
return -1;
}
return _buffer[_currentChar++];
}
static inline int _readInt() {
int c, x, s;
c = _read();
while (c <= 32) c = _read();
x = 0;
s = 1;
if (c == '-') {
s = -1;
c = _read();
}
while (c > 32) {
x *= 10;
x += c - '0';
c = _read();
}
if (s < 0) x = -x;
return x;
}
int main() {
_inputFile = fopen("boxes.in", "rb");
_outputFile = fopen("boxes.out", "w");
int N, K, L, i;
N = _readInt();
K = _readInt();
L = _readInt();
int *p = (int*)malloc(sizeof(int) * (unsigned int)N);
for (i = 0; i < N; i++) {
p[i] = _readInt();
}
fprintf(_outputFile, "%lld\n", delivery(N, K, L, p));
return 0;
}
#endif
