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

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");
int main() {
    int N, K;
    in >> N >> K;
    deque<int> dq;
    long long sum = 0;

    for (int i = 0; i < N; i++) {
        int x;
        in >> x;
        dq.push_back(x);

        if (i >= K - 1) {
            sum += *min_element(dq.begin(), dq.end());

            dq.pop_front();
        }
    }

    out << sum << endl;
    return 0;
}