#include <bits/stdc++.h>

using namespace std;
using ll = long long;

#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define pb push_back
#define ff first
#define sc second
#define int __int128

void solve() {
    ll n, k, t; cin >> n >> k >> t;
    k--;
    vector<ll> a(n);
    for (int i = 0; i < n; i++) cin >> a[i];
    int L = -1, R = 1e9;
    while (R - L > 1) {
        int M = (L + R) / 2;
        vector<int> x(n);
        for (int i = 0; i < n; i++) {
            x[i] = a[i] - 2 * M * i * t;
        }
        int psl = k, psr = k;
        for (int i = k - 1; i >= 0; i--) {
            if (x[i] > x[psl]) psl = i;
        }
        for (int i = k + 1; i < n; i++) {
            if (x[i] < x[psr]) psr = i;
        }
        if (x[psl] < x[psr] || x[0] < x[n - 1]) {
            L = M;
            continue;
        }
        int curl = k, curr = k;
        bool good = true;
        while (curl != psl) {
            int mnl = x[curl], j = curl;
            for (; x[j] <= x[curl]; j--) {
                mnl = min(mnl, x[j]);
            }
            while (curr < n && x[curl] >= x[curr]) {
                if (x[curr] <= mnl) break;
                curr++;
            }
            if (curr >= n || x[curr] > x[curl]) {
                good = false;
                break;
            }
            curl = j;
        }
        if (!good) {
            L = M;
            continue;
        }
        curl = 0;
        curr = n - 1;
        while (curl < psl) {
            int mnl = x[curl], j = curl + 1;
            for (; x[j] < x[curl]; j++) {
                mnl = min(mnl, x[j]);
            }
            while (curr >= k && x[curl] >= x[curr]) {
                if (x[curr] <= mnl) break;
                curr--;
            }
            if (curr < k || x[curr] > x[curl]) {
                good = false; break;
            }
            curl = j;
        }
        if (good) R = M;
        else L = M;
    }
    cout << (ll) R << '\n';
}

signed main() {
    ll tt = 1;
    #ifdef LOCAL 
        freopen("in.txt", "r", stdin);
        freopen("out.txt", "w", stdout);
        cin >> tt;
    #else
        ios::sync_with_stdio(false); 
        cin.tie(0); cout.tie(0);
    #endif

    while (tt--) {
        solve();
    }

    return 0;
}