# Use handshaking lemma

# deg(v) = 2|E|

# Time - O(V)

class Graph:

def __init__(self, vertices):

self.V = vertices

self.graph = [[] for i in range(vertices)]

def add_edge(self, u, v):

self.graph[u].append(v)

self.graph[v].append(u)

def count_edges(self):

s = 0

for i in range(self.V):

s += len(self.graph[i])

return s // 2

g = Graph(9)

g.add_edge(0, 1 )

g.add_edge(0, 7 )

g.add_edge(1, 2 )

g.add_edge(1, 7 )

g.add_edge(2, 3 )

g.add_edge(2, 8 )

g.add_edge(2, 5 )

g.add_edge(3, 4 )

g.add_edge(3, 5 )

g.add_edge(4, 5 )

g.add_edge(5, 6 )

g.add_edge(6, 7 )

g.add_edge(6, 8 )

g.add_edge(7, 8 )

print(g.count_edges())