#include <bits/stdc++.h>
using namespace std;
char getc() {
  char c = getchar();
  while ((c < 'A' || c > 'Z') && (c < 'a' || c > 'z') && (c < '0' || c > '9'))
    c = getchar();
  return c;
}
int gcd(int n, int m) { return m == 0 ? n : gcd(m, n % m); }
int read() {
  int x = 0, f = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9')
    x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
  return x * f;
}
int n, m, k, a[5010], q[5010], head, tail;
long long f[5010][5010];
int main() {
  n = read(), k = read(), m = read();
  for (int i = 1; i <= n; i++) a[i] = read();
  memset(f, 200, sizeof(f));
  f[0][0] = 0;
  for (int j = 1; j <= m; j++) {
    head = 1, tail = 1;
    q[1] = 0;
    for (int i = 1; i <= n; i++) {
      while (head < tail && q[head] < i - k) head++;
      f[i][j] = f[q[head]][j - 1] + a[i];
      while (head <= tail && f[q[tail]][j - 1] <= f[i][j - 1]) tail--;
      q[++tail] = i;
    }
  }
  for (int i = n - 1; i >= max(0, n - k + 1); i--)
    f[n][m] = max(f[n][m], f[i][m]);
  if (f[n][m] < 0)
    cout << -1;
  else
    cout << f[n][m];
  return 0;
}
