#include <fstream>

using namespace std;

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

const int LMAX = 5000000;
long long v[LMAX + 1], dq[LMAX + 1], n, k, st, dr, s;

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