#include <bits/stdc++.h>

using namespace std;

int main() {

    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    int n, k;
    cin >> n >> k;

    vector<int> v(n);
    for(int &x : v)
        cin >> x;

    deque<int> dq; long long ans = 0;
    for (int i = 0; i < k - 1; ++i) {
        while(!dq.empty() && v[dq.back()] >= v[i])
            dq.pop_back();
        dq.push_back(i);
    }

    for (int i = k - 1; i < n; ++i) {
        while(!dq.empty() && v[dq.back()] >= v[i])
            dq.pop_back();
        dq.push_back(i);

        if (i - dq.front() >= k)
            dq.pop_front();

        ans += v[dq.front()];
    }

    cout << ans << endl;

    return 0;
}