#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int>d;
long long a[5000001],k,i,s=0,n,l=0;
int main()
{

    f>>n>>k;
    for(i=1;i<=n;i++) f>>a[i];
    d.push_front(1);
    for(i=2;i<=k;i++)
    {
         if(a[i]>a[d.back()])
        {
            d.push_back(i);
        }
        else
        {
            while(a[i]<a[d.back()])
            {
            d.pop_back();
            }
            d.push_back(i);
        }
    }
    s=s+a[d.front()];
    d.pop_front();
    for(i=k+1;i<=n;i++)
    {
        if(a[i]>a[d.back()])
        {
            d.push_back(i);
        }
        else
        {
            while(a[i]<a[d.back()])
            {
            d.pop_back();
            }
            d.push_back(i);
        }
        if(d.back()-d.front()==k) d.pop_front();
        s=s+a[d.front()];

    }
    g<<s;
    return 0;
}