#include <iostream>
#include <deque>
#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

long v[5000000],n,k;

int main()
{
    int s=0;
    deque<int>my_deq;
    f>>n;f>>k;
    for(int i=1;i<=n;i++)
    {
        f>>v[i];
        while(!my_deq.empty()&&v[my_deq.back()]>=v[i])
          my_deq.pop_back();
        my_deq.push_back(i);
        if(my_deq.front()==i-k)
          my_deq.pop_front();
        if(i>=k)
          s=s+v[my_deq.front()];
    }
    g<<s;
    return 0;
}