#include <fstream>
#include <deque>
using namespace std;
deque <int> d;
int a[5000005], n, k;
long long s;
int main()
{
    ifstream f("dq.in");
    ofstream g("dq.out");
    f >> n >> k;
    for (int i = 1; i <= n; i++)
        f >> a[i];
    for (int i = 1; i <= n; i++)
    {
        while (!d.empty() && a[i] <= a[d.back()])
            d.pop_back();
        d.push_back(i);
        if (d.front() == i - k) d.pop_front();
        if (i >= k) s += a[d.front()];
    }
    g << s;
    return 0;
}