#include <fstream>
#include <deque>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
int n,k,v[500003],sol;
deque <int> d;
int main()
{
      f>>n>>k;
      f>>v[1];
      d.push_back(1);
      for(int i=2;i<=k;++i)
      {
            f>>v[i];
            while(!d.empty()&&v[d.back()]>v[i]) d.pop_back();
            d.push_back(i);
      }
      sol+=v[d[0]];
      for(int i=k+1;i<=n;++i)
      {
            f>>v[i];
            if(d[0]==i-k) d.pop_front();
            while(!d.empty()&&v[d.back()]>v[i]) d.pop_back();
            d.push_back(i);
            sol+=v[d[0]];
      }
      g<<sol;
      return 0;
}