#include<fstream>
#include<deque>

using namespace std;
int i,n,k,x,y,v[5000100];
long long int sum;
deque<int> d;


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

int main()
{
    int s=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
      while(!d.empty()&&v[i]<=v[d.back()])
      d.pop_back();
      d.push_back(i);
      if(d.front()==i-k)
            d.pop_front();
            if(i>=k)
      s+=v[d.front()];
    }
    g<<s<<endl;
}