#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5;
const int mod=10007;
typedef long long ll;

queue<int> q;
int n,m,a[N],ans,sum;

signed main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        //ans=max(ans,a[i]);
    }
    for(int i=1;i<=n;i++){
        while(!q.empty()&&sum<0){
            sum-=a[q.front()];
            q.pop();
        }
        while(!q.empty()&&i-q.front()+1>m){
            sum-=a[q.front()];
            q.pop();
        }
        q.push(i);
        sum+=a[i];
        ans=max(ans,sum);
    }
    cout<<ans;
}