#include <fstream>
#include <deque>
#define nmax 5000001
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
deque < int > dq;

int el, n, k, i, s, j, v[nmax];
int main ()
{
    fin >> n >> k;
    for (i = 1; i <= n; i++)
        fin >> v[i];
    for (i = 1; i <= n; i++)
    {
        while (!dq.empty () && v[i] <= v[dq.back()])
        {
            dq.pop_back ();
        }
        dq.push_back (i);
        if (i - k == dq.front ()) dq.pop_front ();
        if (k <= i) s += v[dq.front()];
    }

    fout << s;
    return 0;
}