#include <bits/stdc++.h>

using namespace std;

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

struct nr
{
    int v,p;
};

long long s;
deque<nr>a;

int main()
{
    int n,k;
    in >> n >> k;
    for (int i = 1; i <= k; i++)
    {
        int x;
        in >> x;
        while (!a.empty() and x <= a.front().v)
            a.pop_front();
        nr aux;
        aux.v = x;
        aux.p = i;
        a.push_front(aux);
    }
    //cout << a.front().v << " ";
    s += a.back().v;
    for (int i = k + 1; i <= n; i++)
    {
        int x;
        in >> x;
        while (!a.empty() and x <= a.front().v)
            a.pop_front();
        nr aux;
        aux.v = x;
        aux.p = i;
        a.push_front(aux);
        while (a.back().p <= i - k)
            a.pop_back();
        //cout << a.front().v << " ";
        s += a.back().v;
    }
    out << s;
    return 0;
}