A quarter, two greatgrandparents or simply one grandparent. My great-grandfather came to Brazil in 1930 married my greatgrandmother, who was of polish origin but brazilian born (lastname Iubel).
In Southern Brazil, there’s a quite big slavic colony, mostly polish, but some russians and ukranians also (and belarussians). There are some cities not far from where I live where most people have polish origins. In the smaller cities, some people are even raised talking polish and only learn portuguese when they have to go to school, but this kind of people is each time getting smaller, the younger generations don’t really feel a connection to their ethnic origins.
In Brazil, people of all kinds were very succesfully culturally assimilated. In the late 30’s and early 40’s (we weere a a dictatorship), many people were arrested for talking in german or italian, places renamed, even one of our main football clubs had to be renamed. Rough times for immigrants.