#include <bits/stdc++.h>

using namespace std;

deque<pair<long long, int>> q;

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