#include <fstream>

using namespace std;

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

int n,k,u,p,v[5000005],deq[5000005],i;
long long s;

int main()
{
    fin >> n >> k ;
    for (i=1;i<=n;i++) fin >> v[i];

    for (i=1;i<=n;i++)
    {
        while (p<=u && v[i]<= v[deq[p]] )
        {
            --u;
        }
        deq[++u]=i;

        if (deq[p]==i-k)
        {
            p++;
        }

        if (i>=k)
        {
            s=s+v[deq[p]];
        }
    }
    fout << s <<endl;

    return 0;
}