Distance from the centre of a graph.

### Example

In this graph, because any vertex can be connected to any other by a chain of two edges, they are all centres of the graph and their distance is 2. Therefore, the radius of this graph is 2.

Distance from the centre of a graph.

In this graph, because any vertex can be connected to any other by a chain of two edges, they are all centres of the graph and their distance is 2. Therefore, the radius of this graph is 2.