#include <fstream>
#include <deque>
using namespace std;

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

int n, k, a[5000001];
long long S;
deque < int > d;

int main()
{
    cin >> n >> k;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    cin.close();

    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()];
    }

    cout << S;
    cout.close();
    return 0;
}