#include <bits/stdc++.h>

using namespace std;
deque<pair<long long, int>>coada;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    long long suma = 0;
    long long n, k, x;
    fin >> n >> k >> x;
    coada.push_back(make_pair(x, 0));
    for (int i = 1; i<k-1; ++i)
    {
        fin >> x;
        while (coada.size() && x <= coada.back().first)
            coada.pop_back();
        coada.push_back(make_pair(x, i));
    }
    for (int i = k-1; i<n; ++i)
    {
        fin >> x;
        while (coada.size() && x <= coada.back().first)
            coada.pop_back();
        coada.push_back(make_pair(x, i));
        while (coada.front().second <= i-k)
            coada.pop_front();
        suma += coada.front().first;
    }
    fout << suma;
    return 0;
}