#include <fstream>
#include <deque>

using namespace std;

int sir[5000005];

int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");

    int n=0,i,k;

    long long int suma=0;
    cin>>n>>k;

    for(i=1;i<=n;i++)
        cin>>sir[i];

    deque<int> coada;
    for(i=1;i<=n;i++)
    {
        while(!coada.empty())
            if(sir[coada.back()]>=sir[i])
                coada.pop_back();
            else
                break;

        coada.push_back(i);
        while(!coada.empty())
            if(i-coada.front()>=k)
                coada.pop_front();
            else
                break;

        if(i>=k)
            suma+=sir[coada.front()];
    }

    cout<<suma<<'\n';

    return 0;
}