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

            s+=d.front().second;
        }
    }
    g<<s;
    return 0;
}