#include <bits/stdc++.h>
#pragma GCC optimize("unroll-loops")
using namespace std;
const long long N = 3e5 + 36;
const long long M = 1e3 + 36;
const long long INF = int(1e9) + 7;
const long long MOD = 987654323;
const long long MOD1 = 1e9 + 7;
const long long MOD2 = 1e9 + 9;
const long long XK[4] = {-1, 0, 1, 0};
const long long YK[4] = {0, 1, 0, -1};
const long long X[8] = {-2, -2, -1, 0, 1, 1, 0, -1};
const long long Y[8] = {0, 1, -2, -2, 0, 1, -1, -1};
mt19937 gen(19937);
struct mem {
  long long num[11], sum = 0, bestL, bestR, bestS;
};
long long a[N], ans = 0;
int sz = 0, n, m, k;
mem b[N], cl;
inline void solve(int n) {
  long long now = b[0].sum, l = 0, r = 0;
  bool f = true;
  ans = max(ans, now);
  ans = max(ans, b[0].bestS);
  while (r + 1 < n) {
    while (now < 0) {
      if (f) {
        now -= b[l].sum;
        now += b[l].bestL;
        f = false;
      } else {
        f = true;
        now -= b[l].bestL;
        ++l;
      }
    }
    ++r;
    now += b[r].sum;
    ans = max(ans, now);
    if (l == r) {
      ans = max(ans, b[l].bestS);
    } else {
      ans = max(ans, now - b[r].sum + b[r].bestR);
    }
  }
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m >> k;
  for (int i(0); i < n; ++i) {
    cin >> a[i];
  }
  mem cl;
  for (int i(0); i < m; ++i) {
    sz = -1;
    for (int j(i); j < n; ++j) {
      if ((j - i) % m == 0) {
        ++sz;
        b[sz].bestS = -k;
        b[sz].bestL = -k;
        b[sz].bestR = -k;
        b[sz].sum = -k;
        for (int i(0); i < m; ++i) {
          b[sz].num[i] = 0;
        }
      }
      b[sz].num[(j - i) % m] = a[j];
      b[sz].sum += a[j];
    }
    ++sz;
    for (int i(0); i < sz; ++i) {
      long long now = b[i].sum;
      for (int j(0); j < m; ++j) {
        now -= b[i].num[j];
        b[i].bestL = max(now, b[i].bestL);
      }
      now = b[i].sum;
      for (int j(m - 1); j >= 0; --j) {
        now -= b[i].num[j];
        b[i].bestR = max(now, b[i].bestR);
      }
      now = b[i].sum;
      for (int I(-1); I < m; ++I) {
        if (I >= 0) now -= b[i].num[I];
        long long klc = now;
        b[i].bestS = max(b[i].bestS, klc);
        for (int j(m - 1); j > I; --j) {
          klc -= b[i].num[j];
          b[i].bestS = max(b[i].bestS, klc);
        }
      }
    }
    solve(sz);
  }
  cout << ans << '\n';
  return 0;
}
