Bob and Candies

Bob is at a candy store. There are $N$ candies in the store. The store of ith candy is $A_i$. The store has some strange rule regarding buying candies. Given integers $L$ and $R$. You can buy a pair of candies if they are atleast L and atmost R distance apart from each other i.e. if you buy ith candy you can buy another candy only in range $[i-R,i-L]$ and $[i+L,i+R]$ of course if it lies in the ra