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

# Author: Maharshi Gor
from collections import deque


def read(type=int):
    return type(input())


def read_arr(type=int):
    return [type(token) for token in input().split()]


def foo(p, u):
    if len(A[u]) == 1 and A[u][0] == p:
        return 0
    H = set()
    E = []
    for v in A[u]:
        if v == p:
            continue
        h = foo(u, v)
        if h == -1:
            return -1
        H.add(h + 1)
        E.append(h + 1)
    if p == -1:
        if len(H) <= 2:
            return sum(H)
        return -1
    else:
        if len(H) == 1:
            return sum(H)
        return -1


n = read()
A = [[] for i in range(n)]
level = [-1] * n

for i in range(n - 1):
    u, v = read_arr()
    u -= 1
    v -= 1
    A[u].append(v)
    A[v].append(u)

# for i in range(n):
#     print(i, ':', end=' ')
#     for v in A[i]:
#         print(v, end=' ')
#     print()

leaves = [i for i in range(n) if len(A[i]) == 1]
parent = [-1] * n
q = deque()

for leaf in leaves:
    q.append(leaf)
    level[leaf] = 0

root = -1

max_level = 0

while len(q) > 0 and root == -1:
    u = q.popleft()
    for v in A[u]:
        if v == parent[u]:
            continue
        if level[v] == -1:
            level[v] = level[u] + 1
            max_level = max(max_level, level[v])
            q.append(v)
            parent[v] = u
        elif level[v] != level[u] + 1:
            root = v if level[v] > level[u] else u
            break

# print('leaves:', leaves)
# print('level:', level)
# print('parent:', parent)
print('root:', root)
if root == -1:
    print(max_level)
else:
    ans = foo(-1, root)
    print(ans)

"""
7
1 2
2 3
2 4
4 5
3 7
1 6
 """

"""
2
1 2
 """
