#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

deque<int> dq;
int v[5000001];

int main()
{
    int n, i, k;
    long long s = 0;
    in >> n >> k;
    for (i=1;i<=n;i++)
    {
        in >> v[i];
        while (!dq.empty() && v[i] < v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (i >= k)
        {
            s+=v[dq.front()];
            if (!dq.empty() && i - dq.front() + 1 >= k)
                dq.pop_front();
        }
    }
    out << s;
    return 0;
}