#include <fstream>
#include <algorithm>
#include <deque>

using namespace std;

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

int n, k;
deque < pair < long long, long long > > DQ;
long long sum;

int main()
{
    int x, i;
    fin >> n >> k;
    for (i = 1; i <= n; ++ i)
        {
         fin >> x;
         if (!DQ.empty() && DQ.front().second <= i - k)
            DQ.pop_front();
         while (!DQ.empty() && DQ.back().first >= x)
            DQ.pop_back();
         DQ.push_back(make_pair(x, i));
         if (i >= k)
            sum += DQ.front().first;
        }
    fin.close();
    fout << sum << "\n";
    fout.close();
    return 0;
}