You have c coins, and you must make n stock transactions. Each transaction involves buying or selling a share. All shares are worth one coin each. You can only buy if you have a coin, and can only sell if you have a share.
Given n and c, print all possible sequences of operations.
Input
Input consists of n and c. Suppose 1 ≤ c ≤ n ≤ 16.
Output
Print in alphabetical order all possible sequences of n operations when we start with c coins. Use ‘b’ to buy and ‘s’ to sell.
Input
4 1
Output
bsbs
Input
7 3
Output
bbbsbsb bbbsbss bbbssbb bbbssbs bbbsssb bbsbbsb bbsbbss bbsbsbb bbsbsbs bbsbssb bbssbbb bbssbbs bbssbsb bsbbbsb bsbbbss bsbbsbb bsbbsbs bsbbssb bsbsbbb bsbsbbs bsbsbsb