#include <fstream>
#include <deque>
using namespace std;
const int nmax = 5000005;
int a[nmax], n, k;
long long sol;
deque <int> d;
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int i;
    fin >> n >> k;
    for(i=1; i<=n; i++)
        fin >> a[i];
    for(i=1; i<=n; i++)
    {
        while(!d.empty() && a[i]<=a[d.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)d.pop_front();
        if(i>=k)sol+=a[d.front()];
    }
    fout << sol;
    fin.close();
    fout.close();
    return 0;
}