#include <fstream>
#define NM 5000005

using namespace std;

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

int n,i,v[NM],be,en,q[NM],k;
long long sum;

int main()
{
    fin >> n >> k;
    be=1;
    for (i=1; i<=n; i++)
    {
        fin >> v[i];
        while (en>=be && v[i]<=v[q[en]])
          en--;
        en++;
        q[en]=i;
        while (be<=en && q[be]<i-k+1)
          be++;
        if (be<=en && i>=k)
          sum+=v[q[be]];
    }
    fout << sum << '\n';
    fin.close();
    fout.close();
    return 0;
}