#include<cstdio>

const int N=1<<23;

int st=0,dr=-1,dq[N],v[N],n,k;

inline void stanga(int i)
{
	if (i-dq[st]==k)
		++st;
}

inline void dreapta(int i)
{
	while (st<=dr && v[i]<=v[dq[dr]])
		--dr;
	dq[++dr]=i;
}

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	long long s=0;
	for (int i=1;i<k;i++)
	{
		scanf("%d",&v[i]);
		dreapta(i);
	}
	for (int i=k;i<=n;i++)
	{
		scanf("%d",&v[i]);
		stanga(i);
		dreapta(i);
		s+=v[dq[st]];
	}
	printf("%lld",s);
	return 0;
}