#include<bits/stdc++.h>
#define ll long long
using namespace std;
int main()
{
    ll n,m;
    cin>>n>>m;
    ll x;
    cin>>x;
    queue<ll> q;
    q.push(x);
    ll sum=x;
    ll ans=sum;
    for(int i=2;i<=n;i++)
    {
        cin>>x;
        if(q.size()==m)
        {
            sum-=q.front();
            q.pop();
        }
        while(sum<0)
        {
            sum-=q.front();
            q.pop();
        }
        q.push(x);
        sum+=x;
        ans=max(ans,sum);
    }
    cout<<ans<<endl;
    return 0;
}