#include <fstream>

using namespace std;

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

const int N = 500000;

int n, k, dq[N], v[N], sum;

int main()
{
    int dr = -1, st = 0;
    in >> n >> k;
    for (int i = 0; i < n; i++) {
        in >> v[i];

        if (dq[st] == i - k) st++;

        while (st <= dr && v[dq[dr]] >= v[i]) dr--;
        dq[++dr] = i;

        if (i >= k - 1) {
            sum += v[dq[st]];
            //out << v[dq[st]] << ' ';
        }
    }
    //out << '\n';
    out << sum;
}