<｜begin▁of▁sentence｜>### Instruction:
Given a graph whose edge set is [(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)], can you find the center of the graph, which is the set of nodes with eccentricity equal to radius?
### Response:
import networkx as nx

# Create a graph
G = nx.Graph()
G.add_edges_from([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])

# Find the center of the graph
center_nodes = nx.center(G)

print('Center of the graph:', center_nodes)
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