Rule 202.3b

The converted mana cost of a transforming double-faced permanent’s back face is calculated as though it had the mana cost of its front face. If a permanent is a copy of the back face of a transforming double-faced card (even if the card representing that copy is itself a double-faced card), the converted mana cost of that permanent is 0. Example: Huntmaster of the Fells is a transforming double-faced card with mana cost {2}{R}{G}. Its converted mana cost is 4. After it transforms to its other face (Ravager of the Fells), its converted mana cost remains 4. Example: A Clone enters the battlefield as a copy of Ravager of the Fells. Its converted mana cost is 0. Example: Insectile Aberration is the back face of a transforming double-faced card whose front face has mana cost {U}. It becomes a copy of Ravager of the Fells. Its converted mana cost becomes 0.

Find this number in the current Rules