#include<fstream>
#include<deque>
using namespace std;
deque<int>dq,p;
int main ()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n,k,i,nr;
    fin>>n>>k;
    for(i=1;i<=k;++i)
    {
        fin>>nr;
        while(!dq.empty() && dq.back()>nr)
        {
            dq.pop_back();
            p.pop_back();
        }
        dq.push_back(nr);
        p.push_back(i);
    }
    long long int sum;
    sum=dq.front();
    for(i=k+1;i<=n;++i)
    {
        fin>>nr;
        if(p.front()==i-k)
        {
            p.pop_front();
            dq.pop_front();
        }
        while(!dq.empty() && dq.back()>nr)
        {
            dq.pop_back();
            p.pop_back();
        }
        dq.push_back(nr);
        p.push_back(i);
        sum=sum+dq.front();
    }
    fout<<sum;
}