#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e5 + 10;
int n, k, t;
int a[N];
long long x[N];
set<long long> L, R;
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cin >> n >> k >> t;
for(int i = 1; i <= n; i++) cin >> a[i];
int l = 0, r = 1e9;
int ans = r;
while(l <= r) {
int mid = (l + r) / 2;
if(2LL * mid * t > 1e9) {
ans = mid;
r = mid - 1;
continue;
}
for(int i = 1; i <= n; i++) x[i] = a[i] - 2LL * mid * i * t;
L.clear();
R.clear();
L.insert(x[k]);
R.insert(x[k]);
int i = k, j = k;
while(true) {
int change = 0;
auto it = R.begin();
if(i > 1) it = R.upper_bound(x[i - 1]);
while(i > 1 && it != R.begin()) {
change++;
i--;
L.insert(x[i]);
if(i > 1) it = R.upper_bound(x[i - 1]);
}
if(j < n) it = L.lower_bound(x[j + 1]);
while(j < n && it != L.end()) {
change++;
j++;
R.insert(x[j]);
if(j < n) it = L.lower_bound(x[j + 1]);
}
if(change == 0) break;
}
if(i != 1 || j != n) {
l = mid + 1;
continue;
}
L.clear();
R.clear();
L.insert(x[1]);
R.insert(x[n]);
if(x[1] < x[n]) {
l = mid + 1;
continue;
}
i = 1, j = n;
while(true) {
int change = 0;
auto it = R.begin();
if(i < k) it = R.upper_bound(x[i + 1]);
while(i < k && it != R.begin()) {
change++;
i++;
L.insert(x[i]);
if(i < k) it = R.upper_bound(x[i + 1]);
}
if(j > k) it = L.lower_bound(x[j - 1]);
while(j > k && it != L.end()) {
change++;
j--;
R.insert(x[j]);
if(j > k) it = L.lower_bound(x[j - 1]);
}
if(change == 0) break;
}
if(i != k || j != k) {
l = mid + 1;
continue;
}
ans = mid;
r = mid - 1;
}
cout << ans;
return 0;
}
