#include<stdio.h>
int n,k,i,sf,inc,v[50010],d[50010];
long long int S;
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d %d",&n,&k);
	inc=1;sf=0;
	for(i=1;i<=n;i++)
		scanf("%d",&v[i]);
	for(i=1;i<=n;i++)
	{
		while(inc<=sf&&v[i]<=v[d[sf]])
			sf--;
		d[++sf]=i;
		if(d[inc]==i-k)inc++;
		if(i>=k)
			S+=v[d[inc]];
	}
	printf("%lld",S);
	return 0;
}