// deque - O(1) amortizat
#include <fstream>
#include <deque>
#define Nmax 5000099
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int N,K,v[Nmax];
long long sol;
deque < int > dq;

int main()
{
     f>>N>>K;
     for(int i=1;i<=N;++i)
     {
          f>>v[i];
          while(!dq.empty() && v[i]<=v[dq.back()])dq.pop_back();
          dq.push_back(i);
          if(dq.front()==i-K)dq.pop_front();
          if(i>=K)
               sol+=v[dq.front()];
     }
     g<<sol<<'\n';
     f.close();g.close();
     return 0;
}