Joe and John are friends, and they are living 60 km from each other.

One day they decide to meet, when they ride their bicycles that afternoon.

They leave their towns at the same time and a butterfly sits onto Joe's nose.

Joe tries to catch it, but it flies to John's nose who is on his way to meet his friend.

He also tries to catch the butterfly who turns back to Joe immediately.

It continues to fluctuate between the two riding friends till they meet.

Find the total distance that the butterfly flew.

(I __think__ that's is what was asked; the wording is terrible.)
Assume the speed of each friend was 10 km/hr and the butterfly's was 20 km/hr.