#include <fstream>
#include <deque>
#define Nmax 5000001
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> d;
int n,k,v[Nmax];
long long int S;
int main()
{
    int i;
    fin>>n>>k;
    for (i=1; i<=n; i++)
        fin>>v[i];
    for (i=1; i<=n; i++)
    {
        while (!d.empty() && v[i]<=d.back())
            d.pop_back();
        d.push_back(v[i]);
        if (i>k)
            if (d.front()==v[i-k])
                d.pop_front();
        if (i>=k)
            S+=d.front();
    }
    fout<<S;
    return 0;
}