#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int n, k, t, a[100100];
ll p[100100];
bool solve(int mid) {
for(int i=1;i<=n;i++) p[i] = a[i]-1ll*t*i*2*mid;
int L = k, R = k;
ll mx = p[k], mn = p[k];
while(1 < L || R < n) {
if(1 < L && p[L-1] >= mn) mx = max(mx, p[--L]);
else if(R < n && mx >= p[R+1]) mn = min(mn, p[++R]);
else break;
}
return 1 == L && R == n;
}
int main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> k >> t;
for(int i=1;i<=n;i++) cin >> a[i];
int l = 0, r = 1e9;
while(l <= r) {
int mid = (l+r)/2;
if(solve(mid)) r = mid-1;
else l = mid+1;
}
cout << l;
}
