#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC push_options
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#include<bits/stdc++.h>
#include <xmmintrin.h>
#include <immintrin.h>
using namespace::std;
__attribute__((constructor))void init(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include<ext/pb_ds/tag_and_trait.hpp>
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// typedef mp::number<mp::cpp_dec_float<0>> cdouble;
// typedef mp::cpp_int cint;
template<typename T>using pbds=__gnu_pbds::tree<T,__gnu_pbds::null_type,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T>using pbds_map=__gnu_pbds::tree<T,T,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T,typename E>using hash_map=__gnu_pbds::gp_hash_table<T,E>;
template<typename T>using pqueue =__gnu_pbds::priority_queue<T, greater<T>,__gnu_pbds::rc_binomial_heap_tag>;
typedef long long lint;
#define INF (1LL<<60)
#define IINF (1<<30)
#define LINF (9223372036854775807LL)
#define EPS (1e-10)
#define endl ('\n')
#define MOD 1000000007LL
//#define MOD 998244353LL
//#define MOD 18446744069414584321ULL
typedef vector<lint> vec;
typedef vector<vector<lint>> mat;
typedef vector<vector<vector<lint>>> mat3;
typedef vector<string> svec;
typedef vector<vector<string>> smat;
template<typename T>inline void numout(T t){bool f=0;for(auto i:t){cout<<(f?" ":"")<<i<INF/2?i:"INF";f=1;}cout<<endl;}
template<typename T>inline void numout2(T t){for(auto i:t)numout(i);}
template<typename T>inline void output(T t){bool f=0;for(auto i:t){cout<<(f?" ":"")<<i;f=1;}cout<<endl;}
template<typename T>inline void output2(T t){for(auto i:t)output(i);}
template<typename T>inline void _output(T t){bool f=0;for(lint i=0;i<t.size();i++){cout<<f?"":" "<<t[i];f=1;}cout<<endl;}
template<typename T>inline void _output2(T t){for(lint i=0;i<t.size();i++)output(t[i]);}
#define rep(i,n) for(lint i=0;i<lint(n);++i)
#define repi(i,a,b) for(lint i=lint(a);i<(lint)(b);++i)
#define rrep(i,n) for(lint i=lint(n)-1;i>=0;--i)
#define rrepi(i,a,b) for(lint i=lint(b)-1;i>=lint(a);--i)
#define irep(i) for(lint i=0;;++i)
#define all(n) begin(n),end(n)
#define dist(a,b,c,d) sqrt(pow(a-c,2)+pow(b-d,2))
inline lint gcd(lint A,lint B){return B?gcd(B,A%B):A;}
inline lint lcm(lint A,lint B){return A/gcd(A,B)*B;}
// inline cint cgcd(cint A,cint B){return B?cgcd(B,A%B):A;}
// inline cint clcm(cint A,cint B){return A/cgcd(A,B)*B;}
bool chmin(auto& s,const auto& t){bool res=s>t;s=min(s,t);return res;}
bool chmax(auto& s,const auto& t){bool res=s<t;s=max(s,t);return res;}
const vector<lint> dx={1,0,-1,0,1,1,-1,-1};
const vector<lint> dy={0,1,0,-1,1,-1,1,-1};
#define SUM(v) accumulate(all(v),0LL)
auto call=[](auto f,auto... args){return f(f,args...);};
template<typename T,typename ...Args>auto make_vector(T x,int arg,Args ...args){if constexpr(sizeof...(args)==0)return vector<T>(arg,x);else return vector(arg,make_vector<T>(x,args...));}

class mint {
  using u64 = std::uint_fast64_t;
    public:
    u64 a;
    constexpr mint(const long long x = 0)noexcept:a(x>=0?x%get_mod():get_mod()-(-x)%get_mod()){}
    constexpr u64 &value()noexcept{return a;}
    constexpr const u64 &value() const noexcept {return a;}
    constexpr mint operator+(const mint rhs)const noexcept{return mint(*this) += rhs;}
    constexpr mint operator-(const mint rhs)const noexcept{return mint(*this)-=rhs;}
    constexpr mint operator*(const mint rhs) const noexcept {return mint(*this) *= rhs;}
    constexpr mint operator/(const mint rhs) const noexcept {return mint(*this) /= rhs;}
    constexpr mint &operator+=(const mint rhs) noexcept {
        a += rhs.a;
        if (a >= get_mod())a -= get_mod();
        return *this;
    }
    constexpr mint &operator-=(const mint rhs) noexcept {
        if (a<rhs.a)a += get_mod();
        a -= rhs.a;
        return *this;
    }
    constexpr mint &operator*=(const mint rhs) noexcept {
        a = a * rhs.a % get_mod();
        return *this;
    }
    constexpr mint operator++(int n) noexcept {
        a += 1;
        if (a >= get_mod())a -= get_mod();
        return *this;
    }
    constexpr mint operator--(int n) noexcept {
        if (a<1)a += get_mod();
        a -= 1;
        return *this;
    }
    constexpr mint &operator/=(mint rhs) noexcept {
        u64 exp=get_mod()-2;
        while (exp) {
            if (exp % 2) {
                *this *= rhs;
            }
            rhs *= rhs;
            exp /= 2;
        }
        return *this;
    }
    constexpr bool operator==(mint x) noexcept {
        return a==x.a;
    }
    constexpr bool operator!=(mint x) noexcept {
        return a!=x.a;
    }
	constexpr bool operator<(mint x) noexcept {
        return a<x.a;
    }
	constexpr bool operator>(mint x) noexcept {
        return a>x.a;
    }
	constexpr bool operator<=(mint x) noexcept {
        return a<=x.a;
    }
	constexpr bool operator>=(mint x) noexcept {
        return a>=x.a;
    }
    constexpr static int root(){
        mint root = 2;
        while(root.pow((get_mod()-1)>>1).a==1)root++;
        return root.a;
    }
    constexpr mint pow(long long n){
        long long x=a;
        mint ret = 1;
        while(n>0) {
            if(n&1)(ret*=x);
            (x*=x)%=get_mod();
            n>>=1;
        }
        return ret;
    }
    constexpr mint inv(){
        return pow(get_mod()-2);
    }
    static vector<mint> fac,ifac;
    static bool init;
    constexpr static int mx=10000001;
    void build(){
        init=0;
        fac.resize(mx);
        ifac.resize(mx);
        fac[0]=1,ifac[0]=1;
        for(int i=1;i<mx;i++)fac[i]=fac[i-1]*i;
        ifac[mx-1]=fac[mx-1].inv();
        for(int i=mx-2;i>=0;i--)ifac[i]=ifac[i+1]*(i+1);
    }
    mint comb(lint b){
        if(init)build();
        if(a==0&&b==0)return 1;
        if((lint)a<b||a<0)return 0;
        return fac[a]*ifac[a-b]*ifac[b];
    }
    mint fact(){
        if(init)build();
        return fac[a];
    }
    mint fact_inv(){
        if(init)build();
        return ifac[a];
    }
    friend ostream& operator<<(ostream& lhs, const mint& rhs) noexcept {
        lhs << rhs.a;
        return lhs;
    }
    friend istream& operator>>(istream& lhs,mint& rhs) noexcept {
        lhs >> rhs.a;
        return lhs;
    }
    constexpr static u64 get_mod(){return MOD;}
};
vector<mint> mint::fac;
vector<mint> mint::ifac;
bool mint::init=1;

template<typename T,typename E>
class segment2d{
    class segment_y{
        E* node;
        int n=1;
        public:
        segment_y(auto sz){
            while(n<=(int)sz)n<<=1;
            node=new E[(n<<1)-1];
            rep(i,(n<<1)-1)node[i]=e;
        }
        T get(auto l,auto r){
            l+=n;r+=n;
            E s=e;
            while(l<r){
                if(l&1)s=f(s,node[l++-1]);
                if(r&1)s=f(s,node[--r-1]);
                l/=2;r/=2;
            }
            return s;
        }
        void update(auto t,E val){
            t+=n-1;
            while(t){
                node[t]=f(node[t],val);
                t=(t-1)>>1;
            }
            node[0]=f(node[0],val);
        }
    };
    vector<vector<pair<T,E>>>node;
    vector<vector<T>>y_list;
    segment_y** seg;
    int n=1,sz;
    vector<pair<T,T>>v;
    vector<T>x_list;
    bool built=0;
    public:
    segment2d(){}
    void add_point(T x,T y){
        x_list.push_back(x);
        v.emplace_back(x,y);
    }
    void update(T x,T y,E val){
        if(!built){
            build();
            built=1;
        }
        x=lower_bound(all(x_list),x)-x_list.begin();
        x+=n-1;
        while(x){
            seg[x]->update(lower_bound(all(y_list[x]),y)-y_list[x].begin(),val);
            x=(x-1)/2;
        }
        seg[0]->update(lower_bound(all(y_list[0]),y)-y_list[0].begin(),val);
    }
    T get(T lx,T rx,T ly,T ry){
        if(!built){
            build();
            built=1;
        }
        lx=lower_bound(all(x_list),lx)-x_list.begin();
        rx=lower_bound(all(x_list),rx)-x_list.begin();
        lx+=n;rx+=n;
        T s=e;
        while(lx<rx){
            if((lx&1)&&y_list[lx-1].size()){
                auto p=lower_bound(all(y_list[lx-1]),ly)-y_list[lx-1].begin();
                auto q=lower_bound(all(y_list[lx-1]),ry)-y_list[lx-1].begin();
                s=f(s,seg[lx-1]->get(p,q));
                ++lx;
            }
            if((rx&1)&&y_list[rx-2].size()){
                rx--;
                auto p=lower_bound(all(y_list[rx-1]),ly)-y_list[rx-1].begin();
                auto q=lower_bound(all(y_list[rx-1]),ry)-y_list[rx-1].begin();
                s=f(s,seg[rx-1]->get(p,q));
            }
            lx/=2;rx/=2;
        }
        return s;
    }
    void build(){
        sort(all(x_list));
        x_list.erase(unique(all(x_list)),x_list.end());
        sz=x_list.size();
        while(n<=sz)n<<=1;
        node.resize((n<<1)-1);
        y_list.resize((n<<1)-1);
        seg=new segment_y*[(n<<1)-1];
        for(auto d:v){
            T x,y;
            tie(x,y)=d;
            _update(lower_bound(all(x_list),x)-x_list.begin(),y);
        }
        rep(i,(n<<1)-1){
            sort(all(y_list[i]));
            y_list[i].erase(unique(all(y_list[i])),y_list[i].end());
            seg[i]=new segment_y(y_list[i].size());
        }
    }
    private:
    void _update(int x,T y){
        x+=n-1;
        while(x){
            y_list[x].emplace_back(y);
            x=(x-1)>>1;
        }
        y_list[0].emplace_back(y);
    }
    constexpr static E e=0;
    constexpr static
    E f(E s,E t){
        return s+t;
    }
};

int main(){
    lint n,k;
    cin>>n>>k;
    vec a(n);
    rep(i,n)cin>>a[i];
    vec b(n+1,0),c(n+1,0);
    rep(i,n)b[i+1]=b[i]+a[i];
    rep(i,n)c[i+1]=c[i]+max(0LL,a[i]);
    lint ans=0;
    rep(i,n-k+1){
        chmax(ans,max(0LL,b[i+k]-b[i])+c[i]+c.back()-c[i+k]);
    }
    cout<<ans<<endl;
}

Measured memory_bytes: 5588