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

#define NMax 5000005

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

deque<int> dq;
int v[NMax];
int n,k;
int sum;

int main()
{
    f>>n>>k;

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

        while(!dq.empty() && dq.front() < i-k+1) dq.pop_front();

        dq.push_back(i);

        if(i >= k) sum += v[dq.front()];
    }

    g<<sum<<"\n";

    f.close();
    g.close();
    return 0;
}