#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

constexpr int NMAX = 5000010;

int64_t a[NMAX];

int main() {
    int n, k;
    fin >> n >> k;

    for (int i = 1; i <= n; i++) {
        fin >> a[i];
    }

    deque<int64_t> q;
    int64_t sum = 0;

    for (int i = 1; i <= n; i++) {
        while (!q.empty() && a[q.back()] > a[i])
            q.pop_back();
        q.push_back(i);

        if (!q.empty() && q.front() < i - k + 1)
            q.pop_front();

        if (i >= k)
            sum += a[q.front()];
    }

    fout << sum;
}