#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<long long> deq;
	vector<long long> v;
	fin>>N>>K;
	//cout<<N<<" "<<K<<endl<<endl;
	
	for(int i=0; i<N; ++i)
	{
		fin>>x;
		v.push_back(x);
		while(!deq.empty() && v[deq.back()]>=x)
		{
			deq.pop_back();
		}
		
		if(!deq.empty())
		{
			if(deq.front()<=i-K)
			{
				//cout<<"-- "<<v[deq.front()]<<" -- "<<endl;
				deq.pop_front();
			}
			if(i>=2)
				S+=v[deq.front()];
		}
		deq.push_back(i);
		
		//cout<<v[i]<<" ";
	}
	cout<<S<<endl;
	
	fin.close();
	fout.close();
	return 0;
}