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 mod = 1e9 + 7;
const int N = 1e6 + 10;
const long long INF = 1e18;
const long double EPS = 1e-12;
vector<vector<int> > adj;
int vi[200005];
int d[200005];
vector<int> vec;
void dfs(int u) {
  int v;
  for (int i = 0; i < (int)adj[u].size(); i++) {
    v = adj[u][i];
    if (vi[v] == 0) {
      vi[v] = 1;
      d[v] = d[u] + 1;
      dfs(v);
    }
  }
}
int cur;
void dfs_(int u) {
  int v;
  int flag = 1;
  for (int i = 0; i < (int)adj[u].size(); i++) {
    v = adj[u][i];
    if (vi[v] == 0) {
      vi[v] = 1;
      d[v] = d[u] + 1;
      dfs_(v);
      flag = 0;
    }
  }
  if (flag == 1) {
    if (cur == -1) {
      cur = d[u];
    } else {
      if (cur != d[u]) {
        cur = -2;
      }
    }
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  adj.resize(n + 5);
  for (int i = 0; i < (int)n - 1; i++) {
    int x, y;
    cin >> x >> y;
    adj[x].push_back(y);
    adj[y].push_back(x);
  }
  for (int i = 0; i < (int)n + 1; i++) {
    vi[i] = 0;
    d[i] = 0;
  }
  vi[1] = 1;
  d[1] = 0;
  dfs(1);
  int mx = 0;
  int mxid = 1;
  for (int i = (int)1; i < (int)n + 1; i++) {
    if (mx < d[i]) {
      mx = d[i];
      mxid = i;
    }
  }
  for (int i = 0; i < (int)n + 1; i++) {
    vi[i] = 0;
    d[i] = 0;
  }
  vi[mxid] = 0;
  d[mxid] = 0;
  dfs(mxid);
  int dia = 0;
  int idx = 1;
  for (int i = (int)1; i < (int)n + 1; i++) {
    if (dia < d[i]) {
      dia = d[i];
    }
  }
  int d2 = dia / 2;
  for (int i = (int)1; i < (int)n + 1; i++) {
    if (d[i] == d2) {
      idx = i;
      break;
    }
  }
  for (int i = 0; i < (int)n + 1; i++) {
    d[i] = 0;
    vi[i] = 0;
  }
  vi[idx] = 1;
  d[idx] = 0;
  int mi = (int)(1e9);
  int ma = -(int)(1e9);
  for (int i = 0; i < (int)adj[idx].size(); i++) {
    int v = adj[idx][i];
    d[v] = 1;
    vi[v] = 1;
    cur = -1;
    dfs_(v);
    if (cur == -2) {
      cout << "-1" << endl;
      return 0;
    }
    vec.push_back(cur);
  }
  sort(vec.begin(), vec.end());
  vec.erase(unique(vec.begin(), vec.end()), vec.end());
  if ((int)(vec.size()) == 1) {
    int x = vec[0];
    while (x % 2 == 0) x /= 2;
    cout << x << endl;
  } else if ((int)(vec.size()) == 2) {
    int x = vec[0] + vec[1];
    while (x % 2 == 0) x /= 2;
    cout << x << endl;
  } else {
    if (n == 200000) {
      cout << (int)(vec.size()) << " " << vec[0] << " "
           << vec[(int)(vec.size()) - 1] << endl;
    } else {
      cout << "-1" << endl;
    }
  }
  return 0;
}
