Accordding to
www.informationfrance.com, " Not officially a
part of France,
Monaco is the second smallest country in the world; only Vatican City is smaller. As such,
Monaco is also the world's smallest monarchy (and principality to be exact)." It doesn't have a boder with Italy, but its border with France is 5.47km according to wikipaedia (" The
border is located between the
French department of Alpes-Maritimes in the
French region of Provence-Alpes-Côte d'Azur and the entire land territory of
Monaco. It is 5.47 kilometres (3.40 mi) in length and is the only land
border Monaco possesses. The
French port of Cap d'Ail
borders Monaco to the southwest. ")
So I assume your answer is less than 5.47km.