#include<iostream>
#include<fstream>
#include<deque>

using namespace std;

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

deque <int> deq;
int v[10000000], k, n;
int s = 0;

int main()
{
    int i;

    f >> n >> k;

    for(i=1; i<=n; ++i)
    {
        f >> v[i];

           while ((!deq.empty()) && (v[deq.back()]>=v[i])
                    deq.pop_back();

           deq.push_back(i);

           if(deq.front() == i+k)
            deq.pop_front();
           if(i >= k)
            s = s + v[deq.front()];
     }

 g << s;

 return 0;
}