#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 1e5 + 10;
ll n, k, t, x[MAXN];
vector<ll> h1, h2, h;
void input() {
cin >> n >> k >> t;
--k;
for (int i = 0; i < n; i++)
cin >> x[i];
}
void calcH() {
for (int i = 0; i < k; i++)
h1.push_back(x[i + 1] - x[i]);
for (int i = n - 1; i > k; i--)
h2.push_back(x[i] - x[i - 1]);
for (int i = 0; i < n - 1; i++) {
if (h1.empty()) {
h.push_back(h2.back());
h2.pop_back();
}
else if (h2.empty()) {
h.push_back(h1.back());
h1.pop_back();
}
else {
if (h1.back() < h2.back()) {
h.push_back(h1.back());
h1.pop_back();
}
else {
h.push_back(h2.back());
h2.pop_back();
}
}
}
}
bool check(ll s) {
ll r = 2 * s * t;
for (auto x : h) {
if (r < x)
return false;
r = (r - x + 2 * s * t);
}
return true;
}
ll findAns() {
ll l = -1, r = 1e9 + 1;
while (r - l > 1) {
ll mid = (l + r) / 2;
if (check(mid))
r = mid;
else
l = mid;
}
return r;
}
int main() {
ios::sync_with_stdio(false); cin.tie(0);
input();
if (n == 1)
cout << 0 << endl;
else {
calcH();
cout << findAns() << endl;
}
return 0;
}
