#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<int>d;
int v[5000001],n,k;
long long s;
int main()
{
   cin>>n>>k;
   for(int i=1;i<=n;i++)
    cin>>v[i];
   d.push_back(1);
   for(int i=2;i<=n;i++)
   {
       while(d.empty()==0&&v[d.back()]>v[i])
        d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        if(i>=k)
            s+=v[d.front()];
   }
   cout<<s;
    return 0;
}