#include <stdio.h>
#define nmax 5000005
struct element{long nr, poz;};
long n, k, x, inc, sf, i;
long long rez;
element co[nmax];

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%ld %ld",&n, &k);
	scanf("%ld",&co[++sf].nr);	co[++inc].poz=1;
	if (k==1)
		rez=co[1].nr;
	for (i=2;i<=n;i++)
	{
		scanf("%ld",&x);
		if (co[inc].poz==i-k)
			inc++;
		while((co[sf].nr>=x)&&(sf>=inc))
			sf--;
		co[++sf].nr=x;	co[sf].poz=i;
		if (i>=k)
				rez+=co[inc].nr;
	}
	printf("%lld",rez);
	return 0;
}