#include <fstream>
#include <algorithm>
#include <queue>
 
using namespace std;
 
ifstream in("deque.in");
ofstream out("deque.out");
 
deque <pair<long,long> > my_deque;
long v[5000001],n,i,k;
long long s=0;
int main()
{

    in >> n >> k;
    for(i = 1 ; i <= n ; i++)
        in >> v[i];
    for(i = 1 ; i<= n ; i++)
    {
        while(my_deque.size())
			if(v[i] < my_deque.back().first)
				my_deque.pop_back();
			else
				break;
        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 << "\n";
    return 0;
}