<｜begin▁of▁sentence｜>### Instruction:
Given a famous 'Zachary' karate club graph, how can we find the optimal number of clusters by analyzing the community structure using VertexDendrogram's optimal_count method?
### Response:
from igraph import Graph
from igraph.clustering import VertexDendrogram

# Load a graph
g = Graph.Famous('Zachary')

# Perform hierarchical clustering on the graph
hd = g.community_edge_betweenness()

# Get a VertexDendrogram object from the hierarchical clustering result
vd = VertexDendrogram(g, hd)

# Find the optimal count for the dendrogram
optimal_count = vd.optimal_count

# Print the optimal count of clusters
print('Optimal number of clusters:', optimal_count)
<|EOT|>
