int n, k;
  cin >> n >> k;
  vector <int> a(n);
  cin >> a;
  vector <int> pref(n), suf(n);
  pref[0] = a[0];
  for (int i = 1; i < n; ++i)
    pref[i] = pref[i - 1] + a[i];
  suf.back() = a.back();
  for (int i = n - 2; i >= 0; --i)
    suf[i] = suf[i + 1] + a[i];
  vector <int> left(n), right(n);
  left[0] = pref[0];
  for (int i = 1; i < k; ++i)
    left[i] = left[i - 1] + a[i];
  for (int i = k; i < n; ++i)
  {
    left[i] = left[i - 1];
    int val = pref[i - 1] - (i - 1 - k >= 0 ? pref[i - 1 - k] : 0);
    val += a[i];
    val -= a[i - k];
    left[i] = max(left[i], val);
  }
  right.back() = suf.back();
  for (int i = n - 2; i >= n - k; --i)
    right[i] = right[i + 1] + a[i];
  for (int i = n - k - 1; i >= 0; --i)
  {
    right[i] = right[i + 1];
    int val = suf[i + 1] - (i + 1 + k < n ? suf[i + 1 + k] : 0);
    val += a[i];
    val -= a[i + k];
    right[i] = max(right[i], val);
  }
  int ans = right[k];
  for (int i = k; i < n; ++i)
  {
    int val = max(left[i - k], i + 1 < n ? right[i + 1] : 0);
    ans = min(ans, val);
  }
  cout << ans;