#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
int n,k,a[100002];
long long s1[100002],s2[100002],s,ans;
int main()
{
	scanf("%d%d",&n,&k);
	for(int i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		s1[i]=s1[i-1]+a[i];
		s2[i]=s2[i-1]+max(0,a[i]);
	}
	ans=max(s1[n]-s1[n-k],0ll)+s2[n-k];
	for(int i=n;i>k;i--)
	{
		s+=max(0,a[i]);
		ans=max(ans,s2[i-k-1]+max(s1[i-1]-s1[i-k-1],0ll)+s);
	}
	printf("%lld",ans);
}