Guests like slippers

Miana and Serdenopis have guests for dinner tonight and thus they have prepared $N$ pairs of slippers for their guests (who shall take off their shoes before entering the house). The slippers are on a line and the $i$-th pair of slippers has size $S_i$. When a guest enters, he takes the first pair of slippers which are still in the line (i.e., they are not taken by a previous guest) and are big e