#include<stdio.h>
#include<algorithm>
#define nmax 50111
using namespace std;

int  n,k,v[nmax],m[nmax],s[nmax],i,sol;

int main(){

	FILE *f = fopen("secv2.in","r");
	FILE *g = fopen("secv2.out","w");
	
	fscanf(f,"%d %d",&n,&k);
	for(i=1; i<=n; i++)
		fscanf(f,"%d",&v[i]);
	
	m[1] = s[1] = v[1];
	for(i=2; i<=n; i++){
		m[i] = min(m[i-1],v[i]);
		s[i] = s[i-1] + v[i];
	}
	
	sol = s[k];
	for(i=k + 1; i<=n; i++)
		sol = max(sol, s[i] - m[i-k]);
	
	fprintf(g,"%d",sol);
	
	fclose(f);
	fclose(g);

	return 0;
}