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

#define MAXN 5000005

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

int n, k;
int a[MAXN];
deque<int> dq;
long long sum;

int main()
{
    f >> n >> k;
    for (int i = 1; i <= n; i++) {
        f >> a[i];
        while (!dq.empty() && a[i] < a[dq.back()]) {
            dq.pop_back();
        }

        dq.push_back(i);

        if (dq.front() < i - k + 1) {
            dq.pop_front();
        }
        if (i >= k) {
            sum += a[dq.front()];
        }
    }
    g << sum << endl;

    return 0;
}