#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
int n, k, x, arr[N];
long long tree[2][17000];
void build(int pos, int l, int r, int dim) {
  if (l == r) {
    if (l <= k)
      tree[dim][pos] = arr[l];
    else
      tree[dim][pos] = -1e18;
    return;
  }
  int mid = (l + r) >> 1;
  build(pos << 1, l, mid, dim);
  build(pos << 1 | 1, mid + 1, r, dim);
  tree[dim][pos] = max(tree[dim][pos << 1], tree[dim][pos << 1 | 1]);
}
void update(int pos, int l, int r, int x, long long v, int dim) {
  if (l == r) {
    tree[dim][pos] = v;
    return;
  }
  int mid = (l + r) >> 1;
  if (mid >= x)
    update(pos << 1, l, mid, x, v, dim);
  else
    update(pos << 1 | 1, mid + 1, r, x, v, dim);
  tree[dim][pos] = max(tree[dim][pos << 1], tree[dim][pos << 1 | 1]);
}
long long get(int pos, int l, int r, int qLow, int qHigh, int dim) {
  if (l >= qLow && r <= qHigh) return tree[dim][pos];
  int mid = (l + r) >> 1;
  long long a = -1, b = -1;
  if (mid >= qLow) a = get(pos << 1, l, mid, qLow, qHigh, dim);
  if (mid + 1 <= qHigh) b = get(pos << 1 | 1, mid + 1, r, qLow, qHigh, dim);
  return max(a, b);
}
int main() {
  scanf("%d%d%d", &n, &k, &x);
  for (int i = 1; i <= n; i++) scanf("%d", &arr[i]);
  for (int i = 1; i <= k; i++) tree[0][i] = arr[i];
  for (int i = k + 1; i <= n; i++) tree[0][i] = -1e18;
  int p = 1;
  for (int z = 2; z <= x; z++) {
    deque<int> q;
    for (int i = max(0, z - k); i < z; i++) {
      while (!q.empty() && tree[!p][i] >= tree[!p][q.back()]) q.pop_back();
      q.push_back(i);
    }
    for (int i = z; i <= n; i++) {
      while (!q.empty() && q.front() < i - k) q.pop_front();
      long long zorbe7 = tree[!p][q.front()];
      while (!q.empty() && tree[!p][i] >= tree[!p][q.back()]) q.pop_back();
      q.push_back(i);
      long long ans = arr[i] + (zorbe7 < 0 ? -1e18 : zorbe7);
      tree[p][i] = ans;
    }
    p = !p;
  }
  long long zorbe7 = -1e18;
  for (int i = n - k + 1; i <= n; i++) zorbe7 = max(zorbe7, tree[!p][i]);
  printf("%lld", zorbe7 > 0 ? zorbe7 : -1);
  return 0;
}
