#include <bits/stdc++.h>

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