Input: the orange gear.
Its number of remained teeth Z1c = 5
Its number of teeth (teeth-completed) Z1 = 18
Its number of cut-off teeth Z1f = Z1 – Z1c = 13
Output: the green gear.
Its number of teeth (teeth-completed) Z2 = 18.
When the orange makes 1 revolution, the green makes 1/3 revolution.