In full mesh topology the number of connections required per given number of nodes grows as a power of 2. General function for the number of connection in full mesh:

f(x)=(x^2-x)/2

x – number of nodes in the network, f(x) – number of connections

So for 2 nodes you need 1 line, for 3 – 3, for 4 – 6, for 5 – 10 etc.