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

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

deque <int > d;
int a[5000005];
long long sum = 0;
int main()
{
    int n, k;
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> a[i];
    for (int i = 1; i <= n; i++)
    {
        while (!d.empty() && a[i] <= a[d.back()])d.pop_back();
        d.push_back(i);
        if (d.front() == i - k)
            d.pop_front();
        if (i >= k) sum += a[d.front()];
    }
    fout << sum << "\n";
    fin.close();
    fout.close();
    return 0;
}