#include <fstream>
#include <queue>

using namespace std;

deque<int> d;

int n, k, s, v[5000010];

int main() {
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >> k;
    for (int i = 1; i <= n; i++) {
        fin >> v[i];
    }
    d.push_back(1);
    if (k == 1) {
        s += v[1];
    }
    for (int i = 2; i <= n; i++) {
        while (!d.empty() && v[d.back()] >= v[i]) {
            d.pop_back();
        }
        d.push_back(i);
        if (d.front() <= i - k) {
            d.pop_front();
        }
        if (i >= k) {
            s += v[d.front()];
        }
    }
    fout << s;
    return 0;
}