#include <fstream>
#include <deque>
#define mk make_pair
using namespace std;

ifstream f("deque.in");
  ofstream g("deque.out");
deque<pair<int, int> >d;
long long sum;
int main()
{int i,val,n,k;
	f>>n>>k;
	
	for(i=0;i<n;i++)
	{
		f>>val;
		 while(!d.empty() && d.back().first>val)
			 d.pop_back();
		 d.push_back(mk(val,i));
		 if(d.front().second+k==i)
			 d.pop_front();
		 sum+=i<k-1?0:d.front().first;
	
	}
	g<<sum<<"\n";

}