#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll dp[2][5005];
int main() {
  cin.tie(0);
  cin.sync_with_stdio(0);
  int n, k, x;
  cin >> n >> k >> x;
  if (n / k > x) return cout << -1, 0;
  vector<int> a(n);
  for (auto &x : a) cin >> x;
  x = min(x, n);
  for (int i = 0; i < k; ++i) dp[1][i] = a[i];
  for (int z = 2; z <= x; ++z) {
    deque<ll> d;
    int c = (z & 1);
    int p = 1 - c;
    int m = min(n, z * k);
    memset(dp[c], 0, sizeof dp[c]);
    for (int i = 0; i < m; ++i) {
      while (d.size() && i - d.front() > k) d.pop_front();
      if (i >= z - 1) dp[c][i] = a[i] + dp[p][d.front()];
      while (d.size() && dp[p][d.back()] <= dp[p][i]) d.pop_back();
      d.emplace_back(i);
    }
  }
  ll ans = 0;
  for (int i = n - 1; i >= 0; --i) {
    if (n - i <= k) {
      ans = max(ans, dp[x & 1][i]);
    } else {
      break;
    }
  }
  cout << ans;
}
