/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int a[]=new int[n+1];
		int k=sc.nextInt();
		for(int i=1;i<=n;i++)
		a[i]=sc.nextInt();
		
		int prefix[]=new int[n+1];
		int suffix[]=new int[n+1];
		
		for(int i=1;i<=n;i++)
		prefix[i]=prefix[i-1]+a[i];
		
		
		suffix[n]=a[n];
		
		for(int i=n-1;i>=1;i--)
		suffix[i]=a[i]+suffix[i+1];
		
		
		int ans=0;
		for(int i=1;i<=n-k;i++)
		{
			ans=Math.max(ans,(prefix[i]+ suffix[(n-k)+i]));
		}
		System.out.println(ans);
	}
}