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

int main()
{
    int N, K, i, x;
    ifstream f("deque.in");
    f >> N >> K;
    deque<pair<int, int>> dq;
    for (i = 0; i < K; i++)
    {
        f >> x;
        while (!dq.empty() && dq.back().first >= x)
            dq.pop_back();
        dq.push_back({x, i});
    }
    long long sum = dq.front().first;

    for (i = K; i < N; i++)
    {
        f >> x;
        if (i - dq.front().second + 1 > K)
            dq.pop_front();
        while (!dq.empty() && dq.back().first >= x)
            dq.pop_back();
        dq.push_back({x, i});
        sum += dq.front().first;
    }
    f.close();

    ofstream g("deque.out");
    g << sum;
    g.close();
    return 0;
}