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;
const int maxn = 2e5 + 7;
vector<int> adj[maxn], adj2[maxn];
int vis[maxn], u, ers[maxn];
bool flag;
int dfs(int u, const int &p, int &d) {
  d++;
  if (adj[u].size() > 2) {
    flag = false;
    return 0;
  }
  for (int i = 0; i < adj[u].size(); i++) {
    int v = adj[u][i];
    if (v == p) continue;
    dfs(v, u, d);
    if (!flag) return 0;
  }
}
void erase(int u, const int &p) {
  ers[u] = true;
  for (int i = 0; i < adj2[u].size(); i++) {
    int v = adj2[u][i];
    if (v == p) continue;
    erase(v, u);
  }
}
int dfs2(int u, const int &p) {
  if (adj[u].size() == 1) return 1;
  set<int> s;
  bool mark = false;
  for (int i = 0; i < adj2[u].size(); i++) {
    int v = adj2[u][i];
    if (v == p) continue;
    int len = dfs2(v, u);
    if (len == -1) {
      mark = true;
      continue;
    }
    if (s.count(len))
      erase(v, u);
    else
      s.insert(len);
  }
  if (mark || s.size() > 1)
    return -1;
  else
    return 1 + *s.begin();
}
int main() {
  ios::sync_with_stdio(false);
  int n, u, v;
  cin >> n;
  for (int i = 1; i < n; i++) {
    cin >> u >> v;
    adj2[u].push_back(v);
    adj2[v].push_back(u);
  }
  dfs2(n >= 2 ? 2 : 1, 0);
  for (int i = 1; i <= n; i++) {
    if (ers[i]) continue;
    for (int j = 0; j < adj2[i].size(); j++) {
      int v = adj2[i][j];
      if (ers[v]) continue;
      vis[i]++;
      vis[v]++;
      adj[i].push_back(v);
    }
  }
  flag = true;
  int m = n;
  for (int i = 1; i <= n; i++) {
    if (ers[i]) {
      m--;
      continue;
    }
    vis[i] /= 2;
    if (vis[i] > 2) {
      flag = false;
      break;
    }
  }
  if (flag) {
    m--;
    while (m % 2 == 0) m /= 2;
    cout << m << endl;
    return 0;
  }
  int l[3];
  flag = false;
  for (int i = 1; i <= n; i++) {
    if (vis[i] == 3 && !ers[i]) {
      flag = true;
      int d = 1;
      for (int j = 0; j < adj[i].size(); j++) {
        int v = adj[i][j];
        l[j] = 1;
        dfs(v, i, l[j]);
      }
      break;
    }
  }
  if (n == 200000) {
    cout << flag << endl;
    return 0;
  }
  if (flag) {
    for (int i = 0; i < 3; i++)
      for (int j = i + 1; j < 3; j++) {
        if (l[i] == l[j]) {
          for (int k = 0; k < 3; k++) {
            if (k != i && k != j) {
              int ans = l[k] + l[i] - 2;
              while (ans % 2 == 0) ans /= 2;
              cout << ans << endl;
              return 0;
            }
          }
        }
      }
    cout << -1 << endl;
  } else
    cout << -1 << endl;
  return 0;
}
