#include <bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define mp(a,b) make_pair(a,b)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;

#define INF INT_MAX/3

#define MAX_N 1000

ll n,k;
ll a[111111];
ll sum[111111];
ll psum[111111];

int main(){
  cin.sync_with_stdio(false);
  cin>>n>>k;
  rep(i,n)cin>>a[i];
  rep(i,n){
    sum[i+1]=sum[i]+a[i];
    psum[i+1]=psum[i]+max(0LL,a[i]);
  }
  ll res=0;
  rep(i,n-k+1){
    maxch(res,max(0LL,sum[i]+sum[n]-sum[i+k]);
  }
  cout<<res<<endl;
  return 0;
}
