/*#include <stdio.h>
int main()
{
int a, i, arr[10001]={},min=23;
scanf("%d", &a);
for(i=1;i<=a;i++)
{
scanf("%d", &arr[i]);
if(arr[i]<min)
{
min=arr[i];
}
}
printf("%d", min);
return 0;
}
*/
#include <stdio.h>
int main()
{
int a, b, i, j, arr[100001]={}, max=-100;
int sum;
scanf("%d %d", &a, &b);
for(i=1;i<=a;i++)
{
scanf("%d", &arr[i]);
}
sum=0;
for(j=1;j<=b;j++)
{
sum+=arr[j];
}
max=sum;
for(i=1;i<=a-b;i++)
{
sum=sum-arr[i]+arr[i+b];
if(max<sum)
{
max=sum;
}
}
printf("%d",max);
return 0;
}