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>
#pragma comment(linker, "/stack:16777216")
using namespace std;
const int INF = 1000000000;
const int BASE = 1000000007;
const int MAX = 200007;
const int MAX2 = 7777;
const int MAXE = 100000;
const int ADD = 1000000;
const int MOD = 1000000007;
const int CNT = 800;
vector<int> G[MAX];
bool ok = 1;
int root = -1;
int res = -1;
int dfs(int v, int p) {
  if (!ok) return -1;
  set<int> S;
  for (int i = (0); i < ((int)G[v].size()); i++) {
    int to = G[v][i];
    if (to == p) continue;
    int c = dfs(to, v) + 1;
    if (!ok) return -1;
    S.insert(c);
  }
  if ((int)S.size() == 0) return 0;
  if ((int)S.size() == 1) {
    if (p == -1) {
      int len = *S.begin();
      while (len % 2 == 0) {
        len /= 2;
      }
      res = len;
      return res;
    }
    return *S.begin();
  }
  if ((int)S.size() > 2) {
    ok = 0;
    return -1;
  }
  if ((int)S.size() == 2) {
    if (p == -1) {
      int len = *S.begin();
      S.erase(S.begin());
      len += *S.begin();
      while (len % 2 == 0) len /= 2;
      res = len;
      return res;
    }
    ok = 0;
    root = v;
    return -1;
  }
}
int main() {
  int n;
  cin >> n;
  for (int i = (0); i < (n - 1); i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    --a;
    --b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  dfs(0, -1);
  if (res > 0) {
    cout << res << endl;
    return 0;
  }
  if (root != -1) {
    ok = 1;
    dfs(root, -1);
  }
  if (res > 0) {
    cout << res << endl;
    return 0;
  }
  cout << -1 << endl;
  return 0;
}
