#include<fstream>
#include<deque>
#include<vector>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,c,a,e,ok;
long long s;
deque<int> d;
vector<int> v;
deque<int>::iterator it,o;
int main()
{ int i;
  f>>n>>k;
  v.reserve(5000001);
  for(i=0;i<n;i++)
	  { f>>a;
	    while(!d.empty()&&v[d.back()]>=a) d.pop_back();
		d.push_back(i);
		v.push_back(a);
		if(d.front()==i-k) d.pop_front();
		if(i>k-2) s+=v[d.front()];
	  }
  g<<s<<'\n';
  f.close(); g.close();
  return 0;
}