#include <fstream>

using namespace std;

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

int dq[5000005];
long long v[50000005];
int n, k;
long long s;
int st, dr = -1;

int main()
{
    in >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        in >> v[i];
    }
    for (int i = 1; i <= n; i++)
    {
        if (st <= dr && dq[st] == i - k)
        {
            st++;
        }
        while (st <= dr && v[i] <= v[dq[dr]])
            dr--;
        dq[++dr] = i;
        if (st <= dr && i >= k)
        {
            s += v[dq[st]];
        }
    }
    out << s << "\n";
    return 0;
}