#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[5000005],st=1,dr=0;
deque <int> q;
long long sol=0;
int main()
{ int i;
    f>>n>>k;
  for(i=1;i<=n;i++)
  { f>>a[i];
      while(!q.empty() && a[i]<a[q.back()]) q.pop_back();
    q.push_back(i);
      while(q.front()<=i-k)
      q.pop_front();
      if (i>=k) sol+=a[q.front()];
  }
  g<<sol;
  return 0;
}