#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int n, k, v[5000001];
long long sum;
deque <int> d;

int main () {
    fin >> n >> k;
    for (int i = 1; i <= n; i++) {
        fin >> v[i];
    }
    for (int i = 1; i <= n; i++) {
        while (!d.empty() && v[i] < v[d.back()])
            d.pop_back();
        d.push_back(i);
        if (d.front() == i-k)
            d.pop_front();
        if (i >= k) {
            //cout << v[d.front()] << " ";
            sum += v[d.front()];
        }
    }
    fout << endl << sum;
}