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

from sys import stdin, stdout

class Node(object):
    def __init__(self, index):
        self.index = index
        self.adjacent = set()
        self.leaf = False
        self.subpathSize=0

    def assessLeaf(self):
        if len(self.adjacent)==0:
            ValueError("Should be at least one neighbour")
        elif len(self.adjacent)==1:
            self.leaf=True
            return True
        return False


n = int(stdin.readline())
treeDict={}

for i in range(n-1):
    n1,n2 = map(int,stdin.readline().rstrip().split())
    if n1 not in treeDict.keys():
        treeDict[n1] = Node(n1)
    if n2 not in treeDict.keys():
        treeDict[n2] = Node(n2)
    treeDict[n1].adjacent.add(n2)
    treeDict[n2].adjacent.add(n1)

pathFound=False

leafList=[]
for i in range(1,n+1):
    if treeDict[i].assessLeaf():
        leafList.append(treeDict[i])
        treeDict[i].subpathSize=0

nodesConsidered=set(leafList)
deadNode=[0]*n
while len(nodesConsidered)>0 and not pathFound:
    nodesConsideredCp=set(list(nodesConsidered))
    nodesConsidered=set()
    for node in nodesConsideredCp:
        if len(node.adjacent)==1:
            nextNode=treeDict[list(node.adjacent)[0]]
            if nextNode in nodesConsideredCp or nextNode in nodesConsidered:
                pathFound=True
                sps=node.subpathSize+nextNode.subpathSize+1
                while sps%2==0:
                    sps=sps/2
                print sps
                break
            nodesConsidered.add(nextNode)
            nextNode.subpathSize=node.subpathSize+1
            nextNode.adjacent.remove(node.index)
            deadNode[node.index-1]=1


if not pathFound:
    print -1
        

