#include <fstream>
#include <deque>
using namespace std;
#define LMAX 5000000
int v[LMAX];
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    int n,k, i;
    long sum = 0;
    deque <int> dq;
    f >> n >> k;
    for (i = 0; i < n; ++i)
        f>> v[i];
    for (i = 0; i < n; ++i)
    {
        while (!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (dq.front() <= i-k)
            dq.pop_front();
        if (i >= k-1)
            sum += v[dq.front()];
    }
    g << sum;
    f.close();
    g.close();
    return 0;
}