#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define all(a) (a).begin(), (a).end()
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
using ld = long double;
template<typename T1, typename T2> bool chkmin(T1 &x, T2 y) { return y < x ? (x = y, true) : false; }
template<typename T1, typename T2> bool chkmax(T1 &x, T2 y) { return y > x ? (x = y, true) : false; }
void debug_out() { cerr << endl; }
template<typename T1, typename... T2> void debug_out(T1 A, T2... B) { cerr << ' ' << A; debug_out(B...); }
template<typename T> void mdebug_out(T* a, int n) { for (int i = 0; i < n; ++i) cerr << a[i] << ' '; cerr << endl; }
#ifdef DEBUG
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define mdebug(a, n) cerr << #a << ": ", mdebug_out(a, n)
#else
#define debug(...) 1337
#define mdebug(a, n) 1337
#endif
template<typename T> ostream& operator << (ostream& stream, const vector<T> &v) { for (auto x : v) stream << x << ' '; return stream; }
template<typename T1, typename T2> ostream& operator << (ostream& stream, const pair<T1, T2>& p) { return stream << p.first << ' ' << p.second; }
const ll inf64 = 1e18;
const int maxN = 10000007;
ll f[maxN];
ll dp[maxN];
ll Ceil(ll a, ll b) {
return a / b + (a % b != 0);
}
ll delivery(int N, int K, int L, int* p) {
int I = 0;
while (I < N && p[I] < (L + 1) / 2) ++I;
for (int i = 0; i < I; ++i) {
f[i + 1] = f[max(0, i + 1 - K)] + 2 * p[i];
}
for (int i = N - 1; i >= I; --i) {
f[i + 1] = f[min(N + 1, i + 1 + K)] + 2 * (L - p[i]);
}
fill(dp, dp + N + 3, inf64);
/*ll ans = L * Ceil(N, K);
for (int i = -1; i < I; ++i) {
for (int j = N; j >= I; --j) {
chkmin(ans, f[i + 1] + f[j + 1] + L * Ceil(j - i - 1, K));
}
}
return ans;*/
for (int i = N - 1; i >= I; --i) {
dp[i + 1] = min(f[i + 1], dp[min(N + 1, i + 1 + K)] + L);
}
ll ans = L * Ceil(N, K);
for (int i = -1; i < I; ++i) {
chkmin(ans, dp[i + 2] + f[i + 1]);
dp[i + 1] = dp[i + 1 + K] + L;
}
return ans;
}
#ifdef DEBUG
signed main() {
#ifdef DEBUG
freopen("in", "r", stdin);
#endif
ios::sync_with_stdio(0);
cin.tie(0);
int N, K, L;
cin >> N >> K >> L;
int* p = new int[N];
for (int i = 0; i < N; ++i) {
cin >> p[i];
}
cout << delivery(N, K, L, p) << '\n';
return 0;
}
#endif
