#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const int nmax=5e6+5;

int n,k,a[nmax];
long long sum;

int main()
{
    f >> n >> k;

    for (int i=1; i<=n; i++ )
      f >> a[i];

    deque <int> dq;

    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() && i-dq.front()+1>k )
              dq.pop_front();

          sum+=a[dq.front()];
       }
    }

    g << sum;
    return 0;
}