// template version 1.2
using namespace std;
#include <iostream>
#include <bits/stdc++.h>

#define infile "../test/sample-1.in"
#define int long long
// #define INF 2147483647
#define INF 1000000000000000000LL
#define MOD 1000000007LL

// {{{ define basic macro
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)(b-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)

#define foreach(x,a) for(auto& (x) : (a) )
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)

#define all(x) (x).begin(),(x).end()
#define sum(v) accumulate(all(v), 0LL)
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
#define ten(n) ((int)1e##n)

template<class T> inline void chmax(T &a, const T &b) { if(a < b) a = b; }
template<class T> inline void chmin(T &a, const T &b) { if(a > b) a = b; }

template<typename A, size_t N, typename T> // n次元配列の初期化。第２引数の型のサイズごとに初期化していく。
void Fill(A (&array)[N], const T &val){
    std::fill( (T*)array, (T*)(array+N), val );
}

template <class T = int>
T in() {T x; cin>>x; return (x);}

struct Fast {
  Fast(){
    std::cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;
// }}}
//{{{ dump macro
#ifdef PCM
  #include "dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif
//}}}
//{{{ others
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;
template<typename T>
using PQ = priority_queue<T, vector<T>, greater<T>>;

int dx[]={1, -1, 0, 0};
int dy[]={0, 0, 1, -1};
//}}}

struct RangeSumVector {
  vector<int> data;
  vector<int> a_sum; //accumulative sum
  RangeSumVector(){}

  int &operator[](int i){
    return data[i];
  }
  void push_back(int v){
    data.push_back(v);
  }

  void calc(){
    a_sum = vector<int>(sz(data));
    a_sum[0] = data[0];
    for(int i=1; i<sz(data); i++){
      a_sum[i] += a_sum[i-1] + data[i];
    }
  }

  int rsum(int l, int r) {  // return sum of [l, r] of data.
    l = std::max(0LL, l);
    r = std::min(r, sz(a_sum)-1);
    if (l > r) return 0;
    return a_sum[r] - (l-1>=0 ? a_sum[l-1] : 0);
  }
};


int solve(){
  int n,k;cin>>n>>k;
  RangeSumVector a, pa;
  int v;
  rep(i, n){
    cin>>v;
    if (v>0){ pa.pb(v); a.pb(v); }
    else{ pa.pb(0); a.pb(v); }
  }
  a.calc();pa.calc();
  dump(a.data, a.a_sum);
  dump(pa.data, pa.a_sum);

  int ans = 0;
  rep(i, n-k+1){
    int res = pa.rsum(0, n-1) - pa.rsum(i, i+k-1);
    dump(i, res, pa.rsum(0, n-1), pa.rsum(i, i+k-1));
    if (a.rsum(i, i+k-1)>0) res += a.rsum(i, i+k-1);
    chmax(ans, res);
  }
  cout << ans << endl;

  return 0;
}

int test(){ //{{{
  return 0;
}
//}}}

signed main() { //{{{
#ifdef INPUT_FROM_FILE
  std::ifstream in(infile);
  std::cin.rdbuf(in.rdbuf());
#endif
#ifdef PCM
  test();
#endif
  solve();
  return 0;
} //}}}


Measured memory_bytes: 3564