Minimum number of moves to light all vertices of a tournament.

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In every vertex of an oriented complete graph (tournament) $G = \langle V, E\rangle$ there is a light bulb. Initally, all of them are turned off. What is the minimum number of moves required to turn on every light bulb? In one move I can choose any vertex $u$ and turn on the light bulb in $u$ and in every neighbour of $u$. I have no idea other than checking all possibilites.