#include <iostream>
using namespace std;
#include <bits/stdc++.h>
int main() {
	// your code goes here
	int n,k;
	cin>>n>>k;
	int arr[n];
	for(int i=0;i<n;i++)
	 {
	 	cin>>arr[i];
	 }
 
	int suffix[n+1];
	suffix[n]=0;
	suffix[n-1]=arr[n-1];
	for(int i=n-2;i>=0;i--)
	 {
	 	suffix[i]=arr[i]+suffix[i+1];
	 }
 
	int ans=suffix[n-k];
 
	int prefixSum=0,t;
	for(int i=0;i<k;i++)
	 {
	 	prefixSum=prefixSum+arr[i];
	 	t=prefixSum+suffix[n-k+(i+1)];
	 	ans=max(ans,t);
	 }
	 cout<<ans;
 
 
 
 
 
 
 
 
 
	return 0;
}

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