#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

int n,k,a;
long long ans;
deque<pair<int,int>> q;

int main()
{
    ifstream f ("deque.in");
    ofstream g ("deque.out");
    f>>n>>k;
    for(int i=1;i<=n;i++){
      f>>a;
      if(q.front().second==i-k)q.pop_front();
      while(not q.empty()&&q.back()>make_pair(a,0))q.pop_back();
      q.push_back(make_pair(a,i));
      //for(auto j:q)cout<<j.first<<" ";cout<<'\n';
      if(i>=k)ans+=(long long)q.front().first;
    }
    g<<ans<<'\n';
    f.close();
    g.close();
    return 0;
}