#include <fstream>
#include <deque>
using namespace std;

#define NMAX 5000000

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

deque<int> d;
int v[NMAX + 1];

int main(int argc, char *argv[])
{
    int n, k;
    long long sum = 0;
    in >> n >> k;
    for (int i = 1; i <= n; ++i) {
        in >> v[i];
        while (!d.empty() && d.front() <= i - k)
            d.pop_front();

        while (!d.empty() && v[d.back()] > v[i])
            d.pop_back();

        d.push_back(i);

        if (k <= i)
            sum += v[d.front()];
    }
    out << sum << endl;
    in.close();
    out.close();
    return 0;
}