#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n, k, v[5000000];
long long s;
deque<int>deq;

int main()
{
    f >> n >> k;
    for(int i = 0; i < n; i++)
    {
        f>>v[i];
        while(deq.size() && v[i] <= v[deq.back()])
            deq.pop_back();
        deq.push_back(i);

        if(i - deq.front() + 1 > k)
         deq.pop_front();

        if(i >= k - 1)
            s += v[deq.front()];
    }
    g << s;
    return 0;
}