#include <bits/stdc++.h>
using namespace std;
int main()
{
int n,k,sum=0,maxsum=0;
cin>>n>>k;
int a[n+1];
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
for(int i=1;i<=n;i++)
{
int b=1;
sum=0;
for(int j=i;j<=i+k-1&&j<=n;j++)
{
sum+=a[j]*b;
b++;
}
if(sum>maxsum)
{
maxsum=sum;
}
}
cout<<maxsum;
}
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