#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<int> dq;
int n,k,i,v[5000001];
long long sum;
int main()
{
    cin>>n>>k;
    for(i=1; i<=n; i++)
    {
        cin>>v[i];
        while(!dq.empty() && v[i]<v[dq.back()])
            dq.pop_back();
        if(dq.front()+k==i)
            dq.pop_front();
        dq.push_back(i);
        if(i>=k && !dq.empty())
            sum+=v[dq.front()];
    }
    cout<<sum;
}