#pragma ide diagnostic ignored "misc-no-recursion"

#include "bits/stdc++.h"

using namespace std;
typedef long long ll;
typedef double db;
typedef pair<int, int> pii;

#define TESTCASE 0

static constexpr int MAXN = 2e5 + 10;

struct DSU {
    vector<int> p, s, f;

    void init(int n) {
        p.assign(n, -1);
        s.assign(n, 1);
        f.resize(n);
        iota(f.begin(), f.end(), 0);
    }

    int find(int x) {
        if (p[x] == -1)
            return x;
        return p[x] = find(p[x]);
    }

    void join(int a, int b) {
        a = find(a);
        b = find(b);
        if (a == b)
            return;
        if (s[a] > s[b])
            swap(a, b);
        p[a] = b;
        s[b] += s[a];
        f[b] = min(f[a], f[b]);
    }
};

int a[2 * MAXN];
int b[2 * MAXN];
DSU dsu;

static void solve([[maybe_unused]] int tc) {
    int N, M, K;
    cin >> N >> M >> K;
    for (int i = 1; i <= N; ++i)
        cin >> b[i];

    dsu.init(1 + N + M);
    ll ans = 0;
    ll asum = 0, bsum = 0;
    for (int i = 1; i <= N + M; i++) {
        bsum += b[i] - (i - M >= 0 ? b[i - M] : 0);
        asum += -(i - M >= 0 ? a[i - M] : 0);
        int pos = i;
        while (asum < bsum && asum < K) {
            pos = dsu.find(pos);
            if (pos <= i - M)
                break;
            int toadd = min(min(bsum, ll(K)) - asum, (ll) b[pos] - a[pos]);
            a[pos] += toadd;
            asum += toadd;
            ans += toadd;
            if (a[pos] == b[pos])
                dsu.join(pos, pos - 1);
        }
    }
    cout << ans << '\n';
}

int main() {
    ios::sync_with_stdio(false);

    if (const char *f = getenv("REDIRECT_STDOUT"); f) {
        freopen(f, "w", stdout);
    }

    int T = 1;
#if TESTCASE
    cin >> T;
#endif

    for (int t = 1; t <= T; t++) {
        solve(t);
    }

    return 0;
}