NiKo and chocolates

NiKo is very fond of eating chocolates . He eats chocolates every day . On day 1 he starts with $1$ chocolate ,and on rest of the days he eats $2$ more chocolates than the previous day. He is concerned about how much money he has spent on his chocolates from day $L$ to day $R$ (both inclusive). You need to help him find how much total money he has spent on chocolates assuming each chocolate cost