#include <fstream>
#include <deque>

using namespace std;
ifstream r("deque.in");
ofstream h("deque.out");
deque <int> d;
int n,k,i,a[5000001];
long long s;
int main()
{
    r>>n>>k;
    for(i=1;i<=n;i++)
    {
        r>>a[i];
    }
    for(i=1;i<=n;i++)
    {
        while(!d.empty()&&a[i]<=a[d.back()]) d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)d.pop_front();
        if(i>=k)
        {
            s+=a[d.front()];
        }
    }
    h<<s;
    return 0;
}