#include <fstream>
#include <deque>

const int NMAX = 50000005;

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int N,K;
int v[NMAX];
long long answer;
deque <int> DD;

int main()
{
    f >> N >> K;
    for (int i = 1; i <= N; ++i)
    {
        f >> v[i];
    }

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

        if (DD.front() < i-K+1)
            DD.pop_front();

        if (i >= K)
        {
            answer += v[ DD.front() ];
        }
    }

    g << answer;

    f.close();
    g.close();

    return 0;
}