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

#define NMAX 5000000

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

int v[NMAX];

deque<int> d;

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() && v[i] < v[d.back()])
            d.pop_back();

        d.push_back(i);
        if (d.front() <= i - k)
            d.pop_front();
        if (i >= k - 1)
            sum +=v[d.front()];
    }

    out << sum << endl;
    in.close();
    out.close();
    return 0;
}