/* 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
{
{
// 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
])); }
}
}
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