#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n, k, a[5000005];
int main()
{
    in >> n >> k;
    for (int i = 1; i <= n; i++) {
        in >> a[i];
    }

    deque<pair<int, int>> q;
    long long sum = 0;

    for (int i = 1; i <= n; i++) {
        while(!q.empty() && q.back().first > a[i])
            q.pop_back();
        q.push_back({a[i], i});
        while (!q.empty() && q.front().second < i - k + 1)
            q.pop_front();

        if (i >= k) {
            sum += q.front().first;
        }
    }

    out << sum << '\n';
    return 0;
}