#include <fstream>
#include <deque>

using namespace std;

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

const int NMAX = 5000000;

int N, K, v[NMAX + 5];
deque <int> dq;

long long sol;

int main()
{
    fin >> N >> K;

    for(int i = 1; i <= N; i++)
        fin >> v[i];

    for(int i = 1; i <= N; i++)
    {
        while(!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();

        dq.push_back(i);

        if(dq.front() == i - K)
            dq.pop_front();

        if(i >= K)
            sol += 1LL * v[dq.front()];
    }

    fout << sol << '\n';

    return 0;
}