#include <bits/stdc++.h>
using namespace std;
inline long long read() {
  long long sum = 0, ff = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') ff = -1;
    ch = getchar();
  }
  while (isdigit(ch)) sum = sum * 10 + (ch ^ 48), ch = getchar();
  return sum * ff;
}
const long long N = 3e5 + 5;
long long n, m, s, ans = -1e12, a[N], f[N][11];
signed main() {
  n = read();
  m = read();
  s = read();
  for (long long i = 1; i <= n; i++) a[i] = read();
  if (m == 1) {
    long long tot = 0;
    for (long long i = 1; i <= n; i++) {
      tot += a[i] - s;
      ans = max(ans, tot);
      tot = max(tot, 0ll);
    }
    printf("%lld\n", max(0ll, ans));
    return 0;
  }
  memset(f, 128, sizeof f);
  for (long long i = 0; i <= n; i++) f[i][0] = 0;
  for (long long i = 1; i <= n; i++)
    for (long long j = 0; j <= min(i, m - 1); j++) {
      if (j == 1)
        f[i][j] = f[i - 1][0] + a[i] - s;
      else if (!j)
        f[i][j] = max(0ll, f[i - 1][m - 1] + a[i]);
      else
        f[i][j] = max(f[i][j], f[i - 1][j - 1] + a[i]);
      ans = max(ans, f[i][j]);
    }
  printf("%lld\n", ans);
  return 0;
}
