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