#include <fstream>
#include <deque>

using namespace std;

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

int n, k, v[5000000];
long long sm;
deque<int> dq;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
    {
        fin >> v[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)
            sm += v[dq.front()];
    }

    fout << sm;

    return 0;
}