#include <fstream>
#include <deque>

#define ll long long

int t[5000000];

int main()
{
    std::ifstream in("deque.in");
    int n, k;
    in >> n >> k;

    for (int i = 0; i < n; i++)
        in >> t[i];
    in.close();

    std::deque<int> dq;
    ll s = 0;

    for (int i = 0; i < n; i++)
    {
        while (!dq.empty() && t[dq.back()] >= t[i])
            dq.pop_back();

        dq.push_back(i);

        if (!dq.empty() && dq.front() <= i - k)
            dq.pop_front();

        if (i >= k - 1)
            s += t[dq.front()];
    }

    std::ofstream out("deque.out");
    out << s;
    out.close();

    return 0;
}