How many seals does a calligraphy work need to be stamped in a calligraphy competition?

Calligraphy works do not need to be stamped. However, suitable seals can add color to the work, including one (name seal), two (name seal and idle seal, or surname seal and idle seal), three (surname seal, name seal and idle seal, and some seals, such as "Changbai Mountain people"). More is redundant.