#include <fstream>
#include <deque>
#define NMAX 5000005

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int i, n, k, v[NMAX];
long long s = 0;
deque < int > d;

int main()
{
    f >> n >> k;

    for (i = 1; i <= n; ++ i)
    {
        f >> v[i];

        while (d.size() && v[i] < v[d.back()])
            d.pop_back();
        d.push_back(i);

        if (i - d.front() == k)
            d.pop_front();

        if (i >= k)
            s += (long long) v[d.front()];
    }

    g << s << '\n';
    return 0;
}