#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque <int> dq;
int v[5000005];
int main()
{
    long long n,k,i,c,sum=0;
    cin>>n>>k;
    c=k;
    k=1-k;
    for(i=1; i<=n; i++)
    {
        cin>>v[i];
        while(dq.empty()==false && dq.front()<=k)
            dq.pop_front();
        while(dq.empty()==false && v[dq.back()]>=v[i])
            dq.pop_back();
        dq.push_back(i);
        k++;
        if(i>=c)
            sum+=v[dq.front()];
    }
    cout<<sum;
    return 0;
}