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

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

int v[5000000],dq[5000000];

int main()
{
    int n,k,sum=0;
    in>>n>>k;
    for(int i=0;i<n;i++)
      {
      in>>v[i];
      }
    int st=0,dr=-1;
    for(int i=0;i<n;i++)
    {
    if(st<=dr&&dq[st]==i-k)
         st++;
      while(st<=dr&&v[i]<=v[dq[dr]])
         dr--;
      dq[++dr]=i;
      if(i>=k-1)
      {
      sum+=v[dq[st]];
      }
    }
    out<<sum;
    return 0;
}