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 = []
        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

def findSubpathSize(leaf,treeDict):
    subpath=[leaf.index]
    subpathFound=True
    pathFound=False
    while subpathFound:
        if len(treeDict[subpath[-1]].adjacent)==1 and len(subpath)==1:
            subpath.append(treeDict[subpath[-1]].adjacent[0])
        elif len(treeDict[subpath[-1]].adjacent)==1:
            pathFound=True
            subpathFound=False
            print len(subpath)-1
        elif len(treeDict[subpath[-1]].adjacent)==2 and treeDict[subpath[-1]].adjacent[0]!=subpath[-2]:
            subpath.append(treeDict[subpath[-1]].adjacent[0])
        elif len(treeDict[subpath[-1]].adjacent)==2:
            subpath.append(treeDict[subpath[-1]].adjacent[1])
        else:
            subpathFound=False
    for nodeId in subpath[:-1]:
        treeDict[nodeId].subpathSize=len(subpath)-1
    return pathFound,subpath
    

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.append(n2)
    treeDict[n2].adjacent.append(n1)

pathFound=False

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

changesMade=True
while changesMade and not pathFound:
    changesMade=False
    terminatesDict={} # Key is the length of the subpath, value is where it terminates
    for leaf in leafList:
        pathFound,subpath=findSubpathSize(leaf,treeDict)
        if pathFound:
            break
        terminatesAt=subpath[-1]
        pathSize=len(subpath)-1
        if pathSize not in terminatesDict:
            terminatesDict[pathSize]=set()
        if terminatesAt not in terminatesDict[pathSize]:
            terminatesDict[pathSize].add(terminatesAt)
        else:
            changesMade=True
            treeDict[terminatesAt].adjacent.remove(subpath[-2])

if not pathFound:
    print -1
        

