#include <fstream>
#include <deque>
using namespace std;

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

deque<int> dq;
deque<int>::const_iterator it, eit;
int sir[5000010];
int N, K;

int main(int argc, char const *argv[])
{
    fin >> N >> K;
    for (int i = 0; i < N; ++i) {
        fin >> sir[i];
    }
    long long result = 0;
    for (int i = 0; i < N; ++i) {
        while (!dq.empty() && sir[i] < sir[dq.back()]) {
            dq.pop_back();
        }
        dq.push_back(i);
        if (!dq.empty() && dq.front() <= i - K) {
            dq.pop_front();
        }
        if (i >= K - 1) {
            result += sir[dq.front()];
        }
        //DEBUG
        // for (it = dq.begin(), eit = dq.end(); it != eit; ++it) {
        //     fout << sir[*it] << ' ';
        // }
        // fout << endl;
        //END DEBUG
    }
    fout << result;
    return 0;
}