#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
deque<int>de;
int v[5000001],n,k,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 (!de.empty() && v[i]<=v[de.back()])
                de.pop_back();
         de.push_back(i);
         if (de.front()==i-k) de.pop_front();
         if (i>=k) s=s+v[de.front()];}
    fout <<s;
    return 0;
}