#include <bits/stdc++.h>
using namespace std;
const long long MOD = 998244353;
const long long MAX = 1e5 + 7;
pair<long long, long long> dp[300001][11];
void solve() {
  long long n, m, k;
  cin >> n >> m >> k;
  long long ar[n + 1];
  for (long long i = 1; i < n + 1; i++) {
    cin >> ar[i];
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if (i - j < 0) {
        break;
      }
      if (j == 1) {
        if (dp[i - 1][m].first <= 0)
          dp[i][j].first = ar[i] - k, dp[i][j].second = 1;
        else
          dp[i][j].first = dp[i - 1][m].first + ar[i] - k,
          dp[i][j].second = dp[i - 1][m].second + 1;
      } else {
        dp[i][j].first = dp[i - 1][j - 1].first + ar[i];
        dp[i][j].second = dp[i - 1][j - 1].second + 1;
      }
    }
  }
  long long ans = -1e18, val;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      ans = max(ans, dp[i][j].first);
    }
  }
  cout << max(ans, (long long)0);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
