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


long long N,K;

ifstream in("deque.in");
ofstream out("deque.out");




int main()
{
	
     long N,K,el,p=1,pos=1,jp_pos=0;
	 long long sum=0;

	 in>>N>>K;
	 deque<long> deq;
	 for(int i=1;i<=N-K+1;i++)
	 {
		while(p<=K)
		{
		    in>>el;
			 while(deq.size() && el<=deq.back())
			 {
				 deq.pop_back();
				 jp_pos++;
			 }
			 if(!deq.size())
			 {
				 pos=pos+jp_pos;
				 jp_pos=0;
			 }
			 deq.push_back(el);
		  p++;
		}
		sum+=deq.front();
		if(i==pos)
		{
			deq.pop_front();
			pos=pos+jp_pos+1;
			jp_pos=0;
		}
		p--;
	 }
	 out<<sum;
	return 0;
}