#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int N, K, a[5000002];
deque < int > Q;
long long sum;

int main()
{
    f>>N>>K;
    for (int i=1; i<=N; ++i)
    {
        f>>a[i];
        while (Q.size() && a[i]<=a[Q.back()])
            Q.pop_back();

        Q.push_back(i);
        if (Q.front()==i-K)
            Q.pop_front();

        if (i>=K)
            sum+=a[Q.front()];
    }
    g<<sum<<'\n';
    return 0;
}