#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long suma=0;
int v[5000005], n, k;
deque <int> deq;
int main()
{
    int i;
    fin>>n>>k;
    for(i=1; i<=n; i++)
        fin>>v[i];
    fin.close();
    for(i=1; i<=n; i++)
    {
        while(!deq.empty() && v[i]<=v[deq.back()])
            deq.pop_back();
        deq.push_back(i);
        if(deq.front()==i-k)
            deq.pop_front();
        if(i>=k)
            suma+=v[deq.front()];
    }
    fout<<suma<<'\n';
    fout.close();
    return 0;
}