#include <bits/stdc++.h>
#define mp(x, y) make_pair(x, y)
#define fi first 
#define se second
using namespace std;
typedef long long ll;

void solve() {
    int n, m, k;
    cin >> n >> m >> k;
    vector<ll> a(n + m + 1), cnt(n + 1);
    for (int i = 1; i <= n; ++i)
        cin >> a[i];
    ll cur = 0;
    ll ans = 0;
    priority_queue<pair<int, ll>> q;
    for (int i = 1; i <= min(n, m); ++i) {
        cnt[i] = min(a[i], k - cur), cur += cnt[i];
        ans += cnt[i];
        if (a[i] - cnt[i] > 0)
            q.push({i, a[i] - cnt[i]});
    }
    // cout << ans << endl;
    for (int i = m + 1; i <= n + m - 1; ++i) {
        cur -= cnt[i - m];
        q.push({i, a[i]});
        while (!q.empty() && cur < k) {
            while (q.top().fi <= i - m)
                q.pop();
            if (q.top().se > k - cur) {
                auto [p, v] = q.top();
                q.pop();
                q.push({p, v - (k - cur)});
                ans += (k - cur);
                cnt[p] += (k - cur);
                cur = k;
            }
            else 
                cnt[q.top().fi] += q.top().se, ans += q.top().se, cur += q.top().se, q.pop();
        }
        // cout << i << ':' << ans << endl;
    }

    cout << ans << '\n';
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    #ifdef LLOCAL
    freopen("a.in", "r", stdin);
    #endif
    // int t;
    // cin >> t;
    // while (t--)
        solve();
    return 0;
}