#include <fstream>
#include <deque>
#include <vector>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque <int> dq;

int main()
{

    int n,k,i;
    long long sum=0;
    cin>>n>>k;
    vector <int> v(n);
    for(i=0;i<n;i++)
    {
        cin>>v[i];
        ///elimin din stanga daca primul nu mai face parte din secv. ultimilor k
        if(!dq.empty() and dq.front()==i-k)
            dq.pop_front();
        ///elimin din dreapta elementele care sigur nu vor mai fi minime
        while(!dq.empty() and v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k-1)
            sum+=v[dq.front()];
    }
    cout<<sum<<"\n";
    return 0;
}