#include <fstream>

using namespace std;

const int N = 5000000;

int v[N], dq[N + 1];

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");

    int n, k, st, dr;
    long long s;
    in >> n >> k;
    st = 1, dr = s = 0;
    for (int i = 0; i < n; ++i)
    {
        in >> v[i];
        if (st <= dr && dq[st] == i - k)
            ++st; //pop back
        while (st <= dr && v[i] <= v[dq[dr]])
            --dr; //pop front
        dq[++dr] = i;
        if (i >= k - 1)
            s += v[dq[st]];
    }
    out << s;

    in.close();
    out.close();
    return 0;
}