#include <fstream>
#include <deque>

using namespace std;

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

struct numar{
    int vl, poz;
};

numar x;

int i, n, k, nr;

long long s;

int main()
{
    deque<numar> md;

    cin >> n >> k;

    for(int i = 1; i <= n; i++)
    {
        cin >> nr;

        while(!md.empty() && md.front().poz < i - k + 1)
        {
            md.pop_front();
        }

        while(!md.empty() && md.back().vl > nr)
        {
            md.pop_back();
        }

        x.vl = nr;
        x.poz = i;

        md.push_back(x);

        if(i >= k)
        {
            s += md.front().vl;
        }

    }

    cout << s << endl;

}