#include <fstream>
#include <queue>

const int NMAX = 5e6 + 1;

int v[NMAX];

int main()
{
    std::ifstream in("deque.in");
    int n{};
    in >> n;
    int k{};
    in >> k;
    for (int i = 0; i < n; ++i)
    {
        in >> v[i];
    }
    in.close();
    std::deque<int> d;
    long long s{0};
    for (int i = 0; i < n; ++i)
    {
        while (!d.empty() && v[i] <= v[d.back()])
        {
            d.pop_back();
        }
        d.push_back(i);
        if (d.front() == i - k)
        {
            d.pop_front();
        }
        if (i >= k - 1)
        {
            s += v[d.front()];
        }
    }
    std::ofstream out("deque.out");
    out << s;
    out.close();
    return 0;
}