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

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

deque <pair <long long, int> > D;
int n,k;
long long rezolva()
{
    fin>>n>>k;
    long long s=0,x;
    fin>>x;
    D.push_back(make_pair(x,1));
    for(int i=2; i<=n; i++)
    {
        fin>>x;
        if(!D.empty())
        {
            if(x>D.back().first)
                D.push_back(make_pair(x,i));
            else
            {
                while(!D.empty()&&D.back().first>=x)
                    D.pop_back();
                D.push_back(make_pair(x,i));
            }


        }
        else D.push_back(make_pair(x, i));
        if(i-k>=D.front().second)
                D.pop_front();
        if(i>=k)
        s+=D.front().first;

    }

    return s;
}
int main()
{
    fout<<rezolva();
    return 0;
}