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

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

# define MAXN 500010

int n, k;
long long sum = 0;
int a[MAXN];
deque<int> coada;

int main()
{
    f >> n >> k;
    for (int i = 1; i <= n; i++) {
        f >> a[i];
    }

    for (int i = 1; i <= n; i++) {
        while(!coada.empty() && a[i] <= a[coada.back()]) {
            coada.pop_back();
        }

        coada.push_back(i);

        if (coada.front() == i - k) {
            coada.pop_front();
        }

        if (i >= k)
            sum += a[coada.front()];
    }
    g << sum << '\n';

    return 0;
}