#include<cstdio>
const int N=1<<22;
int n,k,i,j,st,dr,a[N],dq[N];
long long s=0;
inline void stanga(int i)
{
	if(i-dq[st]==k) st++;
}

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

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