Write a java program, to solve this problem on comments

Rahul is playing a very interesting game. He has N disks ( each of equal radius). 

Every disk has a distinct number out of 1 to N associated with it. Disks are placed one over other in a single pile.

Rahul wants to sort this pile of disk in increasing order from top to bottom. But he has a very very special method of doing this. In a single step he can only choose one disk out of the pile and he can only put it at the top. 

Rahul wants to sort his pile of disks in minimum number of possible steps. So help Rahul in doing so. So don't have to show the actual steps just answer the minimum number of possible steps to sort the pile so that that Rahul can check whether he is doing his work right or wrong