#include <bits/stdc++.h>
#define nmax 50002
using namespace std;

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

int n, k, a[5000004];
long long sum = 0;
deque<int> dq;
int main()
{
    fin >> n >> k;

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

        dq.push_back(i);

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

        if (i >= k)
            sum += a[dq.front()];
    }
    fout << sum;
    return 0;
}