#include <bits/stdc++.h>
using namespace std;

int main() {
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n, k;
    deque<pair<int, int>> q;
    cin >> n >> k;
    long long sum = 0;
    for (int i = 1; i <= n; ++i) {
        int x;
        cin >> x;
        if (i - k == q.front().first) {
            q.pop_front();
        }
        if (q.empty()) {
            q.push_back({i, x});
        } else {
            while (!q.empty() && x < q.back().second) {
                q.pop_back();
            }
            q.push_back({i, x});
        }
        if (i >= k) {
            sum += q.front().second;
        }
    }
    cout << sum;
}