#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int i,v[5000010],n,k;
deque<int> q;
long long S;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];

    for(i=1;i<=n;i++)
    {
        while(!q.empty() && v[i]<=v[q.back()])
            q.pop_back();
            q.push_back(i);
        if(q.front()==i-k)
            q.pop_front();
        if(i>=k)
            S+=v[q.front()];
    }
    fout<<S;
    return 0;
}