10
4 2
7 4
2 6
2 5
4 8
10 3
2 9
9 1
5 10
 10
5 10
7 8
8 3
2 6
3 2
9 7
4 5
10 1
6 4
 4
4 1
4 3
4 2
 3
3 1
1 2
 9
1 2
1 3
1 4
1 5
1 6
6 7
6 8
8 9
 5
1 5
2 3
2 4
1 2
 8
6 1
4 7
4 8
8 5
7 6
4 3
4 2
 7
5 6
5 7
5 1
7 4
6 3
3 2
 3
1 3
3 2
 2
1 2
 5
5 4
4 3
3 1
5 2
 6
1 6
3 1
6 4
5 3
2 5
 11
8 9
2 7
1 11
3 2
9 1
8 5
8 6
5 4
4 10
8 3
 11
11 9
6 7
7 1
8 11
5 6
3 5
9 3
10 8
2 4
4 10
 12
12 6
6 7
8 11
4 8
10 4
12 3
2 10
6 2
12 9
4 1
9 5

-1
 9
 1
 1
 3
 3
 -1
 -1
 1
 1
 1
 5
 1
 5
 -1

#!/usr/bin/env python

n = int(raw_input())

nr_neighbors = [0 for i in xrange(n)]
neighbors = [set([]) for i in xrange(n)]

for i in xrange(n-1):
  u,v = map(int,raw_input().split())
  u-=1
  v-=1
  neighbors[u].add(v)
  neighbors[v].add(u)

nr_neighbors = [len(neighbors[i]) for i in xrange(n)]
leaves = set([i for i in xrange(n) if (nr_neighbors[i] == 1)])

result = 1
while len(leaves) > 0:
  parents = set([])
  for l in leaves:
    parent = list(neighbors[l])[0]
    if parent in parents:
      print result+1
      exit()
    else:
      parents.add(parent)
  
  # Remove leaves
  new_leaves = set([])
  for l in leaves:
    if len (neighbors[l]) == 1:
      parent = neighbors[l].pop()
      neighbors[parent].discard(l)
      nr_neighbors[parent] -= 1
      if nr_neighbors[parent] == 1:
        new_leaves.add(parent)
      elif nr_neighbors[parent] < 1:
        new_leaves.discard(parent)
  leaves = new_leaves
  
  result += 1

print -1
