#3WA求调 88分，不太懂orz

#include <bits/stdc++.h>
using namespace std;
int n,m,sum=-10000000;
int a[500005];
int maxn=-0x3f3f3f3f;
deque <int> q;
int main()
{
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
    }
    for(int i=1;i<=n;i++)
    {
        if(q.size()==m)
        {
            sum-=q.front();
            maxn=max(maxn,sum);
            q.pop_front();
        }
        if(i==1&&a[i]<0) {sum=maxn=a[i];q.push_back(a[i]);}
        if(sum+a[i]>=sum)
        {
            sum=max(sum+a[i],a[i]);
            maxn=max(maxn,sum);
            if(a[i]==sum) q.clear();
            q.push_back(a[i]);
        }
        else
        {
            sum+=a[i];
            q.push_back(a[i]);
        }
    }
    cout<<maxn<<endl;
}