#include <fstream>
#include <algorithm>
#include <queue>

using namespace std;

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

deque<pair<long,long> > my_deque;

int main()
{
    long v[5000001],n,i,k;
    long int s=0;
    in >> n >> k;
    for(i = 1 ; i <= n ; i++)
        in >> v[i];
    for(i = 1 ; i<= n ; i++)
    {
        while(v[i] < my_deque.back().first && my_deque.size())
            my_deque.pop_back();
        my_deque.push_back(make_pair(v[i],i));
        if(my_deque.front().second == i - k)
            my_deque.pop_front();
        if(i >= k)
            s = s + my_deque.front().first;
    }
    out << s;
    return 0;
}