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

#include <bits/stdc++.h>
using namespace std;
vector<int> v[300001];
set<int> s[300001];
bool f[300001];
int deg[300001];
int main() {
  int N;
  scanf("%d", &N);
  int cnt = 0;
  for (int Ni = 1; Ni < N; Ni++) {
    int a, b;
    scanf("%d %d", &a, &b);
    v[a].push_back(b);
    v[b].push_back(a);
  }
  for (int Ni = 1; Ni <= N; Ni++) deg[Ni] = v[Ni].size();
  queue<int> que;
  for (int Ni = 1; Ni <= N; Ni++)
    if (deg[Ni] == 1) que.push(Ni), s[Ni].insert(0);
  int p;
  while (!que.empty()) {
    int t = que.front();
    que.pop();
    f[t] = true;
    int num = *s[t].begin();
    for (int vi = 0; vi < v[t].size(); vi++)
      if (!f[v[t][vi]]) {
        p = v[t][vi];
        if (s[p].find(num + 1) != s[p].end()) {
          cnt += num + 1;
        }
        s[p].insert(num + 1);
        deg[p]--;
        if (deg[p] == 1 && s[p].size() == 1) que.push(p);
      }
  }
  int sum = 0;
  for (int x : s[p]) sum += x;
  if (sum + cnt == N - 1 && s[p].size() <= 2) {
    while (sum % 2 == 0) sum /= 2;
    printf("%d\n", sum);
  } else
    puts("-1");
}
