#include <fstream>
#include <deque>
#include <utility>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

deque< pair <int,int> >d;

int main()
{
    long long n,k,x,i,sum=0;
    cin>>n>>k;
    for(i=1; i<=n; i++)
    {
        cin>>x;
        while(x<=d.front().first&&d.size()>0)
        {
            d.pop_front();
        }
        d.push_front(make_pair(x,i));
        if(i>=k)
            sum=sum+d.back().first;
        if(d.back().second==i-k+1)
        {
            d.pop_back();
        }
    }
    cout<<sum;
    return 0;
}