#include <fstream>
#include <deque>
using namespace std;
int v[5000500];
deque<int> dq;

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n,k,i;
    long long s=0;
    in>>n>>k;
    for(i=1;i<=n;++i){
      in>>v[i];
      while(!dq.empty() && v[dq.back()]>v[i]) dq.pop_back();
      dq.push_back(i);
      if(i-dq.front()==k) dq.pop_front();
      if(i>=k) s=s+v[dq.front()];
    }
    out<<s;
    return 0;
}