#include <fstream>
#include <deque>
#define tip long long

using namespace std;
deque< pair< tip,tip > > q;
ifstream f("deque.in");
ofstream g("deque.out");
tip n,k,i,sol,a;
int main()
{
    f>>n>>k;
    for(i=1;i<=k;i++)
    {
        f>>a;
        while(a<q.front().first&&q.size())
            q.pop_front();
        q.push_front(make_pair(a,i));
    }
    sol=q.back().first;
    for(i=k+1;i<=n;i++)
    {
        f>>a;
        while(a<q.front().first&&q.size())
            q.pop_front();
        q.push_front(make_pair(a,i));
        if(q.back().second<=i-k)
            q.pop_back();
        sol+=q.back().first;
    }
    g<<sol;
    return 0;
}