#include <fstream>
#include <deque>

using namespace std;

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

int n, k, i, x;
long long int s;
deque<pair<int, int> > dq;

int main()
{
    s = 0;

    f >> n >> k;
    for(i = 1; i <= n; i++)
    {
        f >> x;

        while(!dq.empty() && dq.back().first > x)
            dq.pop_back();
        dq.push_back(make_pair(x, i));
        while(!dq.empty() && dq.front().second <= i - k)
            dq.pop_front();
        if(i >= k)
            s += dq.front().first;
    }

    g << s << "\n";

    f.close();
    g.close();

    return 0;
}