#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int a,n,k,i;
deque <int> c;
long long solutie;
int main()
{
    deque <int> ind;
    fin>>n>>k;
    for(i=1;i<=k;++i)
    {
        fin>>a;
        while(c.size()>0&&a<=c.back())
        {
            c.pop_back();
            ind.pop_back();
        }
        c.push_back(a);
        ind.push_back(i);
    }
    solutie=solutie+c.front();
    for(i=k+1;i<=n;++i)
    {
        fin>>a;
        while(a<=c.back()&&c.size()>0)
        {
            c.pop_back();
            ind.pop_back();
        }
        c.push_back(a);
        ind.push_back(i);
        if(i-ind.front()==k)
        {
            c.pop_front();
            ind.pop_front();
        }
        solutie=(long long)solutie+c.front();;
    }
    fout<<solutie;
    fin.close();
    fout.close();
    return 0;
}