#include <fstream>
#include <deque>
using namespace std;
ifstream fi("deque.in");
ofstream fo("deque.out");
struct nod{
     int val;
     int poz;
}y;
deque < nod > dq;
int n,i,j,k,s,x;
long long mini;

int main()
{
   fi>>n>>k;
   for(i=1;i<=n;i++){
      fi>>x;
      while(!dq.empty() and dq.back().val>x)
           dq.pop_back();
      y.val=x;
      y.poz=i;
      dq.push_back(y);
      if(dq.front().poz<i-k+1)
         dq.pop_front();
      if(i>=k)   mini+=dq.front().val;
   }
  fo<<mini;
  return 0;
}