#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int Deque[5000010],a[5000010],Front,Back,i,n,k;
long long Sum;
int main()
{
    fin>>n>>k;
    Front=1;
    Back=0;
    for(i=1;i<=n;i++)
        fin>>a[i];
    for(i=1;i<=n;i++)
    {
        while(a[i]<=a[Deque[Back]]&&Front<=Back)
            Back--;
        Deque[++Back]=i;
        if(Deque[Front]==i-k)
            Front++;
        if(i>=k)
            Sum+=a[Deque[Front]];
    }
    fout<<Sum;
    return 0;
}