#include <iostream>
#include <queue>
#include <cstring>
using namespace std;

using int64 = long long;

int main() {
    int N, M, K;
    cin >> N >> M >> K;

    const int MAXN = 200005;

    static int64 A[MAXN];
    for (int i = 0; i < N; i++) {
        cin >> A[i];
    }

    static int64 dp[2][MAXN];
    memset(dp, -1, sizeof(dp));
    dp[0][0] = 0;
    for (int i = 0; i < N; i++) dp[1][i] = A[i];

    int64 ans = 0;
    // スライド最大値
    for (int i = 1; i < K; i++) {
        deque<int> dq;
        for (int j = 0; j < N; j++) {
            if (dq.empty() or dp[i & 1][dq.front()] < 0) dp[(i + 1) & 1][j] = -1;
            else {
                dp[(i + 1) & 1][j] = dp[i & 1][dq.front()] + int64(i + 1) * A[j];
            }
            while (!dq.empty() and dp[i & 1][dq.back()] <= dp[i & 1][j]) dq.pop_back();
            dq.push_back(j);

            if (dq.front() == j - M) dq.pop_front();

            if (i == K - 1) ans = max(ans, dp[K & 1][j]);
        }
    }
    cout << ans << endl;

    return 0;
}