#include <fstream>
#include <deque>
#include <tuple>

using namespace std;

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

deque<pair<int,int>>deq;
int n,x,k,ans;

int main()
{
    fin >>n >>k;
    for(int i = 1; i <= n; i++)
    {
        fin >>x;
        if(!deq.empty())
        {
            while(x < deq.back().first)
            {
                deq.pop_back();
                if(deq.empty())
                {
                    break;
                }
            }
        }
        deq.push_back({x,i});
        if(deq.front().second <= deq.back().second-k)
        {
            deq.pop_front();
        }
        if(i >= k)
        {
            ans+=deq.front().first;
        }
    }
    fout <<ans;
    return 0;
}