Distributing chocolates

Aakash likes distributing chocolates to children on his girlfriend's birthday. He has $N$ boxes of chocolates with him. Each box $i$ has $a$i chocolates. There are $N$ children standing in a line to get a box of chocolates. Each child gets one box of chocolate. Giving a box of $x$ chocolates to a child takes $x$ amount of time. Each child has to wait until all the children standing before him/her