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

int N, K, a[5000002];
long long sol=0;
deque <int> Q;

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) sol+=a[Q.front()];
    }
    g<<sol<<'\n';
    return 0;
}