#include <fstream>
#include <deque>


using namespace std;

struct numbers{
    int value;
    int indice;
};

deque <numbers> deque;





int main() {
    ifstream inputfile("deque.in");
    ofstream outputfile("deque.out");

    int n, k;
    inputfile >> n >> k;
    int result = 0;
    for (int i = 0; i <= n; i++)
    {
        numbers x;
        inputfile >> x.value;
        x.indice = i + k;
        while ( deque.size() && deque.back().value > x.value)
        {
            deque.pop_back();
        }
        deque.push_front(x);

        if(i >= k - 1) result += 1LL * deque.front().value;
    }

    outputfile << result;
    return 0;
}