#include <cstdio>
int sir[5000100],deque[5000100];
int n,k,min;
long long rez;

int main()
{
	freopen ("deque.in","r",stdin);
	freopen ("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	for (int i=1;i<=n;++i)
		scanf("%d",&sir[i]);
	int st=1,dr=1,i=2;
	deque[1]=1;
	while (i<=k)
	{
		while (sir[i]<=sir[deque[dr]]&&dr)
			--dr;
		deque[++dr]=i;
		++i;
	}
	rez=(long long)sir[deque[1]];
	while (i<=n)
	{
		while (sir[i]<=sir[deque[dr]]&&dr>=st)
			--dr;
		deque[++dr]=i;
		while (deque[st]<=i-k)
			++st;
		rez+=(long long)sir[deque[st]];
		++i;
	}
	printf("%lld",rez);
	return 0;
}