#include <fstream>
#include <deque>

using namespace std;

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

struct elem
{
    int v, p;
};

deque<elem> d;
int n, k, x;
long long sol;

int main()
{
    fin >> n >> k;
    for(int i = 1; i < k; ++i)
    {
        fin >> x;
        d.push_back({x, i});
    }
    for(int i = k; i <= n; ++i)
    {
        fin >> x;
        while(!d.empty() && x <= d.back().v)
            d.pop_back();
        d.push_back({x, i});
        if(d.front().p == i - k)
            d.pop_front();
        sol += d.front().v;
    }
    fout << sol;
    return 0;
}