#include <fstream>
#include <deque>
#define NMAX 5000001
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> dq;
int n,k;
int a[NMAX];
long long int suma;
int main()
{
    int i;
    fin>>n>>k;
    for (i=1; i<=n; i++)
            fin>>a[i];
    for (i=1; i<=n; i++)
    {
        if (!dq.empty() && dq.front()==i-k) dq.pop_front();
        while (!dq.empty() && a[dq.back()]>a[i])
                    dq.pop_back();

        dq.push_back(i);
        if (i>=k) suma+=a[dq.front()];
    }
    fout<<suma<<'\n';

    return 0;
}