#include <bits/stdc++.h>

using namespace std;

struct Initializer {
  Initializer() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15);
  }
} initializer;

template<typename Value> class CumulativeSum1D {
private:
  struct RangeValue {
    int i, j;
    Value v;
    RangeValue(int i, int j, Value v) : i(i), j(j), v(v) {}
  };

  vector<Value> val;
  vector<RangeValue> rangeValue;

public:
  CumulativeSum1D(int n) : val(n + 2, Value(0)) {}

  template<typename T> CumulativeSum1D(T v) {
    val.resize(v.size() + 2, Value(0));
    partial_sum(v.begin(), v.end(), val.begin() + 1);
  }

  void add(int i, Value v) {
    add(i, i + 1, v);
  }

  void add(int i, int j, Value v) {
    rangeValue.emplace_back(i, j, v);
  }

  // [i,j)
  Value sum(int i, int j) {
    if (!rangeValue.empty()) {
      adjacent_difference(val.begin(), val.end(), val.begin());
      adjacent_difference(val.begin(), val.end(), val.begin());
      for (const auto& v : rangeValue) {
        val[v.i + 1] += v.v;
        val[v.j + 1] -= v.v;
      }
      partial_sum(val.begin(), val.end(), val.begin());
      partial_sum(val.begin(), val.end(), val.begin());
      rangeValue.clear();
    }
    return val[j] - val[i];
  }

  Value value(int i) {
    return sum(i, i + 1);
  }
};

template<typename T> bool chmin(T& a, T b) {return a > b ? a = b, true : false;}

template<typename T> bool chmax(T& a, T b) {return a < b ? a = b, true : false;}

template<typename T> istream& operator>>(istream &s, vector<T> &v) {
  for (T &t : v) s >> t;
  return s;
}

template<typename T> ostream& operator<<(ostream &s, const vector<T> &v) {
  for (const T &t : v) s << t << endl;
  return s;
}

template<typename T> T min(vector<T>& v) {return *min_element(v.begin(), v.end());}

template<typename T> T max(vector<T>& v) {return *max_element(v.begin(), v.end());}

template<typename T> int min_element(vector<T>& v) {return min_element(v.begin(), v.end()) - v.begin();}

template<typename T> int max_element(vector<T>& v) {return max_element(v.begin(), v.end()) - v.begin();}

template<typename T> void sort(vector<T>& v) {sort(v.begin(), v.end());}

template<typename T, typename Function> void sort(vector<T>& v, Function func) {sort(v.begin(), v.end(), func);}

template<typename T> void rsort(vector<T>& v) {sort(v.rbegin(), v.rend());}

template<typename T> void reverse(vector<T>& v) {reverse(v.begin(), v.end());}

template<typename T> void unique(vector<T>& v) {v.erase(unique(v.begin(), v.end()), v.end());}

template<typename T> void nth_element(vector<T>& v, int n) {nth_element(v.begin(), v.begin() + n, v.end());}

template<typename T> bool next_permutation(vector<T>& v) {return next_permutation(v.begin(), v.end());}

template<typename T> int find(vector<T>& v, T t) {return find(v.begin(), v.end(), t) - v.begin();}

template<typename T> int in(vector<T> v, T t) {return find(v, t) != int(v.size());}

template<typename T> int lower_bound(vector<T>& v, T t) {return lower_bound(v.begin(), v.end(), t) - v.begin();}

template<typename T> int upper_bound(vector<T>& v, T t) {return upper_bound(v.begin(), v.end(), t) - v.begin();}

template<typename T> T accumulate(const vector<T>& v, function<T(T, T)> func = plus<T>()) {return accumulate(v.begin(), v.end(), T(), func);}

template<typename T> void adjacent_difference(vector<T>& v) {adjacent_difference(v.begin(), v.end(), v.begin());}

template<typename T> void adjacent_difference(vector<T>& v, vector<T>& u) {adjacent_difference(v.begin(), v.end(), u.begin());}

template<typename T> void partial_sum(vector<T>& v, vector<T>& u) {partial_sum(v.begin(), v.end(), u.begin());}

template<typename T> T inner_product(vector<T>& v, vector<T>& u) {return inner_product(v.begin(), v.end(), u.begin(), T(0));}

template<typename T> int count(const vector<T>& v, T t) {return count(v.begin(), v.end(), t);}

template<typename T, typename Function> int count_if(const vector<T>& v, Function func) {return count_if(v.begin(), v.end(), func);}

template<typename T, typename Function> void remove_if(vector<T>& v, Function func) {v.erase(remove_if(v.begin(), v.end(), func), v.end());}

template<typename T, typename Function> bool all_of(vector<T> v, Function func) {return all_of(v.begin(), v.end(), func);}

template<typename T, typename Function> bool any_of(vector<T> v, Function func) {return any_of(v.begin(), v.end(), func);}

template<typename T, typename Function> bool none_of(vector<T> v, Function func) {return none_of(v.begin(), v.end(), func);}

template<typename T> vector<T> subvector(vector<T>& v, int a, int b) {return vector<T>(v.begin() + a, v.begin() + b);}

template<typename T> int kinds(const vector<T>& v) {return set<T>(v.begin(), v.end()).size();}

template<typename T> void iota(vector<T>& v, T t = 0) {iota(v.begin(), v.end(), t);}

template<typename T> bool is_sorted(const vector<T>& v) {return is_sorted(v.begin(), v.end());}

int main() {
  int n, k;
  cin >> n >> k;
  vector<int64_t> a(n);
  cin >> a;
  CumulativeSum1D<int64_t> sum1(a), sum2(n);
  for (int i = 0; i < n; ++i) sum2.add(i, max(a[i], int64_t(0)));
  int64_t res = 0;
  for (int i = 0; i + k <= n; ++i) {
    chmax(res, max(sum1.sum(i, i + k), int64_t(0)) + sum2.sum(0, n) - sum2.sum(i, i + k));
  }
  cout << res << endl;
}



Measured memory_bytes: 5752