#include <stdio.h>

int main()
{
 long v[100001],mn=0,n,k,i,min=0,max=0;
 freopen("perle2.in","r",stdin);
 freopen("perle2.out","w",stdout);
 scanf("%ld%ld",&n,&k);
 v[0]=0;
 for (i=1;i<n+1;i++)
 {
	scanf("%ld",&v[i]);
	v[i]+=v[i-1];
	if (v[i]<min) {min=v[i];mn=i;}
	if ((v[i]-min>max)&&(i-mn+1>=k)) max=v[i]-min;
 }
 printf("%ld",max);
 return 0;
}