#include <fstream>
#include <deque>

using namespace std;
typedef unsigned int uint;

ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    uint n,k;
    fin >> n >> k;

    deque<uint> dq;

    long long v[n], sum = 0;
    for (uint i = 0; i < n; ++i)
    {
        fin >> v[i];

        while (!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();

        dq.push_back(i);

        if (i + 1 >= k)
        {
            if (dq.front() + k == i)
                dq.pop_front();

            sum += v[dq.front()];
        }
    }

    fout << sum;
}