#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

deque <int> D;
int N, K, X[5000005];
long long S;

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

int main()
{
    int i;
    fin >> N >> K;
    for (i=1; i<=N; ++i)
    {
        fin >> X[i];
        while (!D.empty () && X[D.back ()]>=X[i])
        {
            D.pop_back ();
        }
        D.push_back (i);
        if (D.front ()<=i-K)
        {
            D.pop_front ();
        }
        if (i>=K)
        {
            S+=X[D.front ()];
        }
    }
    fout << S << "\n";
    fin.close ();
    fout.close ();
    return 0;
}