#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <pair <int,int> >q;
int main()
{
    int n,k,x,i;
    long long s=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>x;
        while(q.empty()==false && x<q.back().first)
        {
            q.pop_back();
        }
        q.push_back({x,i});
        if(i>=k)
        {
            s=s+q.front().first;
            if(i-k+1==q.front().second)
            {
                q.pop_front();
            }
        }
    }
    g<<s;
    return 0;
}