#include<fstream>
#include<queue>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque <long long> d;
int k;
long long s , n , v[5000001];
void dreapta(int p)
{
    while(!d.empty() && v[p]<=v[d.back()])
    {
        d.pop_back();
    }
    d.push_back(p);
}
void stanga(int p)
{
    if(d.front()==p-k)
        d.pop_front();
}
int main()
{
    in>>n>>k;
    for(int i=1;i<k;i++)
    {
        in>>v[i];
        stanga(i);
        dreapta(i);

    }
    for(int i=k;i<=n;i++)
    {
        in>>v[i];
        stanga(i);
        dreapta(i);
        s+=v[d.front()];
    }
    out<<s;
}