#include <bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque <int> d;
int v[5000001];
int main()
{
	long long n,ans=0,k;
	in>>n>>k;
	for(int i=0;i< n;i++)
	{
		in>>v[i];
	}
	for(int i=0;i< n;i++)
	{
		while(!d.empty() and d.front()==i-k  )
			d.pop_front();
		while(!d.empty() and v[i]<=v[d.back()])
			d.pop_back();
		d.push_back(i);
		if(i>=k-1)
		{
			ans+=v[d.front()];
		}
	}
	out<<ans;
}