#include<cstdio>
struct ddd
{
	int val,poz;
}deq[5000000];

int n,k,i,st,dr,x;

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