#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>

namespace nachia{

template<class Val>
struct DequeOperateAggregation{
private:

    Val me;
    std::vector<Val> A[2];
    std::vector<Val> Prod[2];

    void recalcProd(){
        Prod[0].resize(A[0].size() + 1, me);
        for(std::size_t i=0; i<A[0].size(); i++) Prod[0][i+1] = A[0][i] + Prod[0][i];
        Prod[1].resize(A[1].size() + 1, me);
        for(std::size_t i=0; i<A[1].size(); i++) Prod[1][i+1] = Prod[1][i] + A[1][i];
    }
public:

    DequeOperateAggregation(Val e)
        : me(std::move(e))
    {
        recalcProd();
    }
    void pushFront(Val v){
        A[0].push_back(std::move(v));
        Prod[0].push_back(A[0].back() + Prod[0].back());
    }
    void pushBack(Val v){
        A[1].push_back(std::move(v));
        Prod[1].push_back(Prod[1].back() + A[1].back());
    }
    void popFront(){
        if(A[0].empty()){
            int lessHalf = A[1].size() / 2;
            A[0] = std::vector<Val>(A[1].rbegin() + lessHalf, A[1].rend());
            A[1] = std::vector<Val>(A[1].end() - lessHalf, A[1].end());
            recalcProd();
        }
        A[0].pop_back();
        Prod[0].pop_back();
    }
    void popBack(){
        if(A[1].empty()){
            int lessHalf = A[0].size() / 2;
            A[1] = std::vector<Val>(A[0].rbegin() + lessHalf, A[0].rend());
            A[0] = std::vector<Val>(A[0].end() - lessHalf, A[0].end());
            recalcProd();
        }
        A[1].pop_back();
        Prod[1].pop_back();
    }
    Val allProd(){ return Prod[0].back() + Prod[1].back(); }
};

} // namespace nachia

using namespace std;
using i64 = long long;
#define rep(i,n) for(int i=0; i<(int)(n); i++)
const i64 INF = 1001001001001001001;

struct S { i64 a=-INF; int i=-1; };
S operator+(S l, S r){ return l.a > r.a ? l : r; }

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int N, K; cin >> N >> K;
    vector<i64> A(N); rep(i,N) cin >> A[i];
    vector<i64> sumA(N+2); rep(i,N) sumA[i+1] = sumA[i] + A[i];
    sumA[N+1] = sumA[N];
    nachia::DequeOperateAggregation<S> Q({ -INF, -1 });
    Q.pushBack({ -sumA[0] });
    Q.pushBack({ -sumA[1] });
    i64 ans = 0;
    rep(i,N){
        auto s = Q.allProd();
        i64 a = s.a + sumA[i+1];
        Q.pushBack({ a - sumA[i+2] });
        ans = max(ans, a);
        if(i >= K-2) Q.popFront();
    }
    cout << ans << '\n';
    return 0;
}