15
3 5 2         // vertex 0's neighbors
0 4 7 11      // vertex 1's neighbors 
              // vertex 2's neighbors (none)
0 1 4 6       // vertex 3's ...
9 2 4 5 0     // vertex 4's ...
0 4 7 9 10    // vertex 5's ...
1 3 7 12      // vertex 6's ...
8 2 1         // vertex 7's ...
7 0 10 11     // vertex 8's ...
0 1 2 3 4 5   // vertex 9's ...
3 4 9 11      // vertex 10's ...
5 8 14        // vertex 11's ...
13 0          // vertex 12's ...
10            // vertex 13's ...
12            // vertex 14's ...