#include<bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define pb push_back
#define all(a) begin(a),end(a)
#define allr(a) rbegin(a),rend(a)
#define ff first
#define ss second
template<class T> bool chmax(T& a,T b){return a<b?a=b,1:0;}
template<class T> bool chmin(T& a,T b){return a>b?a=b,1:0;}
using ll =long long;
using pii =pair<int,int>;
using pll=pair<long long,long long>;
using vi=vector<int>;
using vll=vector<ll>;
inline bool ingrid(int a,int b,int h,int w){
    return 0<=a&&a<h&&0<=b&&b<w;
}

const int INFI = numeric_limits<int>::max() / 2; const long long INFL = numeric_limits<long long>::max() / 2;
constexpr pii dx4[4] = {pii{-1, 0}, pii{0, -1},pii{1, 0}, pii{0, 1} };
#define endl '\n'

template< typename T, typename Compare = less< T >, typename RCompare = greater< T > >
struct PrioritySumStructure {

  size_t k;
  T sum;

  priority_queue< T, vector< T >, Compare > in, d_in;
  priority_queue< T, vector< T >, RCompare > out, d_out;

  PrioritySumStructure(int k) : k(k), sum(0) {}

  void modify() {
    while(in.size() - d_in.size() < k && !out.empty()) {
      auto p = out.top();
      out.pop();
      if(!d_out.empty() && p == d_out.top()) {
        d_out.pop();
      } else {
        sum += p;
        in.emplace(p);
      }
    }
    while(in.size() - d_in.size() > k) {
      auto p = in.top();
      in.pop();
      if(!d_in.empty() && p == d_in.top()) {
        d_in.pop();
      } else {
        sum -= p;
        out.emplace(p);
      }
    }
    while(!d_in.empty() && in.top() == d_in.top()) {
      in.pop();
      d_in.pop();
    }
  }

  //上位 k 個の和（要素数がk個未満の場合すべての要素の和）
  T query() const {
    return sum;
  }

  //要素 x を追加する
  void insert(T x) {
    in.emplace(x);
    sum += x;
    modify();
  }

  //要素 x を削除する
  void erase(T x) {
    assert(size());
    if(!in.empty() && in.top() == x) {
      sum -= x;
      in.pop();
    } else if(!in.empty() && RCompare()(in.top(), x)) {
      sum -= x;
      d_in.emplace(x);
    } else {
      d_out.emplace(x);
    }
    modify();
  }

  //k を指定しなおす
  void set_k(size_t kk) {
    k = kk;
    modify();
  }
  
  //k を返す
  size_t get_k() const {
    return k;
  }

  //全体の要素数を返す
  size_t size() const {
    return in.size() + out.size() - d_in.size() - d_out.size();
  }
};

//降順 k 個に指定
template< typename T >
using MaximumSum = PrioritySumStructure< T, greater< T >, less< T > >;

//昇順 k 個に指定
template< typename T >
using MinimumSum = PrioritySumStructure< T, less< T >, greater< T > >;
template<typename T,typename F>
struct SegmentTree{
private:
    int n;
    vector<T> data;
    const F f;
    T ti;
public:
    SegmentTree()=default;
    SegmentTree(int n,F f,T ti):n(n),f(f),ti(ti),data(n<<1,ti){}
    SegmentTree(vector<T> v,F f,T ti):n(v.size()),f(f),ti(ti),data(n<<1,ti){
        for(int i=0;i<n;i++)data[i+n]=v[i];
        for(int i=n-1;i>=1;i--)data[i]=f(data[i<<1],data[i<<1|1]);
    }
    void update(int k,const T& val){
        k+=n;
        data[k]=val;
        for(k>>=1;k>=1;k>>=1){
            data[k]=f(data[k<<1],data[k<<1|1]);
        }
    }
    const T operator[](const int &k){return data[k+n];}
    void apply(int k,const T& val){
        update(k,f(data[k+n],val));
    }
    const T prod(int l,int r){
        l+=n;r+=n;
        T vl=ti,vr=ti;
        for(;l<r;l>>=1,r>>=1){
            if(l&1)vl=f(vl,data[l++]);
            if(r&1)vr=f(data[--r],vr);
        }
        return f(vl,vr);
    }
};
template<typename T,typename F>
SegmentTree<T,F> get_SegmentTree(int n,F f,T ti){return SegmentTree<T,F>(n,f,ti);}
template<typename T,typename F>
SegmentTree<T,F> get_SegmentTree(vector<T> v,F f,T ti){return SegmentTree<T,F>(v,f,ti);}

ll n,k;
vll a;
void solve(){
    vll pref(n+1);
    rrep(i,n-1,0){
        pref[i]=a[i]+pref[i+1];
    }
    MaximumSum<ll> q(k-1);
    rep(i,1,k-1){
        q.insert(pref[i]);
    }
    auto seg=get_SegmentTree(pref,[](ll a,ll b){return min(a,b);},INFL);
    ll ans=-INFL;
    rep(i,k-1,n){
        q.insert(pref[i]);
        chmax(ans,pref[0]+q.query()-seg.prod(i+1,n+1)*k);
    }
    cout<<ans<<endl;
}

int main(){
    cin>>n>>k;
    a.resize(n);
    rep(i,0,n)cin>>a[i];
    solve();
    return 0;
}
/*
上位k-1個の和を管理しながら
区間minをとる
*/