#include "boxes.h"
#include <bits/stdc++.h>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
long long din[20000003],v[20000003],dininv[20000003];
long long sol=1e18;
long long delivery(int n, int k, int l, int p[]) {
int i;
for (i=1;i<=n;i++)
{
v[i]=p[i-1];
}
for (i=1;i<=k;i++)
{
din[i]=v[i]*2;
}
for (i=k+1;i<=n;i++)
{
din[i]=2*v[i]+din[i-k];
}
for (i=n;i>=n-k+1;i--)
{
dininv[i]=2*(l-v[i]);
}
for (i=n-k;i>=1;i--)
{
dininv[i]=2*(l-v[i])+dininv[i+k];
}
for (i=0;i<=n;i++)
{
sol=min(sol,din[i]+dininv[i+1]);
}
for (i=0;i<=n;i++)
{
sol=min(sol,din[i]+dininv[i+k+1]+l);
}
return sol;
}
#ifdef HOME
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 // HOME
