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