#include<fstream>
#include<iostream>
#include<vector>
#include<deque>
using namespace std;

typedef long long int64;

int main()
{
	long N,K,x;
	int64 S=0;
	fstream fin("deque.in", fstream::in);
	fstream fout("deque.out", fstream::out);
	deque<pair<long,long> > deq;
	fin>>N>>K;
	//cout<<N<<" "<<K<<endl<<endl;
	
	for(int i=1; i<=N; ++i)
	{
		fin>>x;
		while(!deq.empty() && deq.back().second>=x)
			deq.pop_back();
		deq.push_back(make_pair(i,x));
		
		while(!deq.empty() && deq.front().first<=i-K)
		{
			//S+=deq.front().second;
			deq.pop_front();
		}
		if(i>=3)
			S+=deq.front().second;

	}
	fout<<S<<endl;
	
	fin.close();
	fout.close();
	return 0;
}