#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque <int> coada;
int n,k,x,mi=INT_MAX,v[5000005];
long long s;
int main()
{
    in >> n >> k;
    for(int i=1; i<=n; i++)
    {
        in >> v[i];
    }
    for(int i=1; i<=n; i++)
    {
        while(!coada.empty() && v[i]<=v[coada.back()])
        {
            coada.pop_back();
        }
        coada.push_back(i);
        if(coada.front()==i-k)
        {
            coada.pop_front();
        }
        if(coada.back()>=k)
        {
            s+=v[coada.front()];
        }
    }
    out << s;
    return 0;
}