#include<fstream>
#include<deque>
using namespace std;
int a[5000010],n,k;
long long suma;
deque <int> D;
int main()
{
	int i;
	ifstream fin("deque.in");
	fin>>n>>k;
	for(i=1;i<=n;i++)
		fin>>a[i];
	fin.close();
	for(i=1;i<=n;i++)
	{
		while( !D.empty() && a[D.back()]>=a[i])
			D.pop_back();
		D.push_back(i);
		if(D.front()==i-k)
			D.pop_front();
		if(i>=k)
			suma=suma+a[D.front()];
	}
	ofstream fout("deque.out");
	fout<<suma<<"\n";
	fout.close();
	return 0;
}