#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const int N=1e5+9;
int a[N];
ll sum=0;

int main()
{
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	
	int n;cin>>n;
	for(int i=1;i<=n;++i)cin>>a[i];
	int k,p;//个数,间隔
	cin>>k>>p;
	int cnt=0;
	ll max_val=-1;
	int j=1;
	for(int i=j;i<=n;i+=p)
	{
		cnt++;
		sum+=a[i];
		if(cnt==k)
		{
			max_val=max(max_val,sum);
			j++;
			i=j;
			cnt=0;
			sum=0;
		}
	}
	cout<<max_val;
	return 0;
}