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

import sys
from collections import defaultdict
from collections import Counter

def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

def solve():
    n = int(input())
    Adj = [[] for i in range(n)]
    for i in range(n - 1):
        u, v = map(int, input().split())
        u, v = u - 1, v - 1
        Adj[u].append(v)
        Adj[v].append(u)

    # debug(Adj, locals())
    path_ls = defaultdict(Counter)

    trace_deg1(n, Adj, path_ls)

    # debug(path_ls, locals())

    min_ = float('inf')

    for u in path_ls:
        if len(path_ls[u]) == 1:
            if path_ls[u][l] >= 2:
                min_ = min(min_, l)

    if min_ == float('inf'):
        ans = -1
    else:
        ans = min_

    print(ans)

def trace_deg1(n, Adj, path_ls):
    for u in range(n):
        if len(Adj[u]) == 1:
            # debug(u, locals())
            path_l = 2
            v = Adj[u][0]

            while len(Adj[v]) == 2:
                path_l += 1
                v, u = sum(Adj[v]) - u, v

            path_ls[v][path_l] += 1

    return None


if __name__ == '__main__':
    solve()