#include <fstream>
#include <deque>

using namespace std;

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

int n, k, v[5000010];
deque<int> d;
long long s;

void insereaza(int x);
void sterge(int i);

int main()
{
    int i;
    fin >> n >> k;
    for (i = 1; i <= k - 1; i++)
    {
        fin >> v[i];
        insereaza(i);
    }
    for (i = k; i <= n; i++)
    {
        fin >> v[i];
        sterge(i);
        insereaza(i);
        s += (long long)v[d.front()];
    }
    fout << s << '\n';
    fout.close();
    return 0;
}

void insereaza(int x)
{
    while (!d.empty() && v[x] < v[d.back()])
            d.pop_back();
    d.push_back(x);
}
void sterge(int i)
{
    while (d.front() <= i - k)
        d.pop_front();
}