#include <bits/stdc++.h>

using namespace std;

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

deque <int> coada;
int n, a[5000005], k;
long long sum = 0;

int main()
{
    fin >> n >> k;
    for (int i = 1; i <= n; ++i)
    {
        fin >> a[i];
    }
    for (int i = 1; i <= n; ++i)
    {
        while (coada.size() > 0 && a[i] < a[coada.back()]) coada.pop_back();
        coada.push_back(i);
        if (i > k && coada.size() > 0)
        {
            if (coada.front() == i - k) coada.pop_front();
        }
        if (i >= k)
        {
            if (coada.size() > 0)
                sum = sum + a[coada.front()];
        }
    }
    fout << sum;
    return 0;
}