In a process I have 3-4 user input tasks in series those are assigned to differe

In a process I have 3-4 user input tasks in series those are assigned to different groups.What i want to achieve is that the 4th task in the series must be assigned to the person who has completed the first task in the process where as first task initially is being assigned to a specific group.In a nutshell,i need to know the person inside a group who has completed a user input task and then dynamically i want to assign next task to the same person.
Any pointers will be really helpful for me....

OriginalPostID-80448

OriginalPostID-80448