#include<iostream>
#include<fstream>
#include<deque>
using namespace std;
deque <int> deq;
long long v[10000000],k,n,suma=0;
int main()
{ifstream f("deque.in");
 ofstream g("deque.out");
 f>>n;
 f>>k;
 for(int i=1;i<=n;i++)
     {f>>v[i];
      while(!deq.empty() && v[deq.back()]>=v[i])
        deq.pop_back();
      deq.push_back(i);
      if(deq.front()==i-k)
        deq.pop_front();
      if(i>=k)
        suma=suma+v[deq.front()];
     }
 g<<suma;
 return 0;
}