#include <fstream>
#include <deque>
using namespace std;
ifstream cin ("deque.in");
ofstream cout ("deque.out");

struct numar{
    int val;
    int poz;
};
long long int s,n,x,k;
numar nr;
deque<numar>mydeq;

int main()
{
    cin>>n>>k;
        for (int i=1;i<=n;i++)
        {
            cin>>x;
            while (!mydeq.empty() && mydeq.front().poz<i-k+1)
                mydeq.pop_front();
            while (!mydeq.empty() && x<mydeq.back().val)
                mydeq.pop_back();
            nr.poz=i;
            nr.val=x;
            mydeq.push_back(nr);
            if (i>=k)
                s+=mydeq.front().val;
        }
    cout<<s;

    return 0;
}