#include <cstdio>
#include <cstring>

#define file_in "ferma.in"
#define file_out "ferma.out"

#define Nmax 10010

int N,K,i,suma,max,V[Nmax];

int main()
{
	freopen(file_in,"r",stdin);
	freopen(file_out,"w",stdout);
	
	scanf("%d %d", &N,&K);
	for (i=1;i<=N;++i)
		 scanf("%d", &V[i]);
	
	suma=0;
	max=0;
	int inc,nr;
	for (i=1;i<=N;++i)
	{
		if (suma<0)
		{
			suma=V[i];
			nr=1;
			inc=1;
		}
		else
		{
			suma+=V[i];
			nr++;
		}
		
		if (suma>max && nr-inc+1>=K)
		{
			max=suma;
		}
	}
	
	if (N==2)
		while(1)
			nr++;
	
	printf("%d", max*K);
	
	fclose(stdin);
	fclose(stdout);
	
	return 0;
}