Table Problem : solve this six persons problem

An interesting puzzle concerns six people, named Adam, Barry, Carly, Darlene, Edgar and Fyodor, who are seated around a table. There are six chairs. In front of one of the chairs is a computer, which each person has a short turn on. They proceed like this: Adam uses the computer first. After finishing, Barry uses the computer, and Adam occupies the seat that Barry previously sat in. After Barry finishes, Carly has her turn, and Barry now sits in Carly’s seat.

Initially, they are seated like this (with Adam seated in front of the computer):

How many turns at the computer (excluding Adam’s initial turn) are needed for everyone to be back in their original seating?

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SOLUTION: 

Thirty turns. After the first ‘round’ of turns A will be seated in B’s original seat, B will be in C’s original seat, C will be in D’s original seat, and so on. After the second round, F will be in B’s original seat, A will be in C’s original seat, B will be in D’s original seat, and so on. So we’re essentially moving backwards through the alphabet with each set of six turns. Continuing in this manner, we see that five sets of turns are necessary to have everyone back in their original seats, meaning 30 turns in total are required.