#include<stdio.h>
#include<deque>
#include<utility>
using namespace std;
deque<pair<int,int> > Q;
int n,k;
void read(),solve();
int main()
{
	read();
	solve();
	return 0;
}
void read()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
}
void solve()
{
	long long S=0;
	int i,v;
	for(i=1;i<k;i++)
	{
		scanf("%d",&v);
		while(!Q.empty()&&v<Q.back().second)Q.pop_back();
		Q.push_back(make_pair(i,v));
	}
	for(i=k;i<=n;i++)
	{
		scanf("%d",&v);
		while(!Q.empty()&&v<Q.back().second)Q.pop_back();
		Q.push_back(make_pair(i,v));
		if(Q.front().first==i-k)Q.pop_front();
		S+=Q.front().second;
	}
	printf("%lld\n",S);
}