#include "bits/extc++.h"

using namespace std;

template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
    cerr << t;
    ((cerr << " | " << u), ...);
    cerr << endl;
}

#ifdef DEBUG
#define dbg(...)                                           \
    cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
         << ": ";                                          \
    dbgh(__VA_ARGS__)
#else
#define cerr   \
    if (false) \
    cerr
#define dbg(...)
#endif

#define endl "\n"
#define long int64_t
#define sz(x) int(std::size(x))

void solve() {
    int n, m, kv;
    cin >> n >> m >> kv;

    int arr[n];
    for (auto& a : arr) {
        cin >> a;
    }

    int pay[n] {}, cpayed = 0;
    long ans = 0;
    vector<pair<int, int>> avail;

    for (int i = 0; i < n + m; i++) {
        if (i >= m) {
            cpayed -= pay[i - m];
        }
        if (i < n) {
            avail.emplace_back(i, arr[i]);
        }

        while (cpayed < kv && sz(avail)) {
            auto& [ind, amt] = avail.back();
            if (ind <= i - m) {
                avail.clear();
                break;
            }

            int sub = min(amt, kv - cpayed);
            pay[ind] += sub;
            amt -= sub;
            cpayed += sub;
            ans += sub;
            if (!amt) {
                avail.pop_back();
            }
        }
    }

    for (int i = 0; i < n; i++) {
        dbg(pay[i]);
    }
    cout << ans << endl;
}

int main() {
    cin.tie(nullptr);
    cin.exceptions(ios::failbit);
    ios_base::sync_with_stdio(false);
    solve();
}