#include "deque"
#include "fstream"

using namespace std;

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

int N, K;

struct elem{
    int value, pos;
};

int main() {

    deque<elem> dq;

    fin >> N >> K;

    long long sum = 0;
    int x;
    for(int i = 1 ; i <= N ; i++) {
        fin >> x;
        while(!dq.empty() && x <= dq.back().value) {
//            fout << "Removing: " << dq.back().value << "\n";
            dq.pop_back();
        }
        elem e = {x, i};
//        fout << "Adding: " << x << "\n";
        dq.push_back(e);
        if(i >= K) {
//            fout << "Position: " << dq.front().pos << "\n";
            if(i - dq.front().pos >= K) {
                dq.pop_front();
            }
//            fout << "Sum: " << sum << "\n";
//            fout << "Front added : " << dq.front().value << "\n";
            sum += dq.front().value;
//            fout << "Sum: " << sum << "\n";
        }
    }

    fout << sum;

    return 0;
}