#include <fstream>

using namespace std;
const int N=5000000;
int d[N],v[N],n,k;
ifstream cin("deque.in");
ofstream cout("deque.out");
int main()
{
    int n,i,k,s=0;
    cin>>n>>k;
    int st=0,dr=1;
    for(i=0;i<n;i++)
    {
      cin>>v[i];
      if(d[st]==i-k)
      {
        st++;
      }
      while(st<=dr&&v[i]<=v[d[dr]])
      {
        dr--;
      }
      d[++dr]=i;
      if(i>=k-1)
          s+=v[d[st]];
    }
    cout<<s;
    return 0;
}