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;
long long MOD = 1e9 + 7;
vector<int> v[200001], h;
bool visited[200001];
int l, dist;
set<int> s;
int dfs(int id, int d) {
  visited[id] = 1;
  if (id != 1 and v[id].size() == 1) {
    if (dist < d) {
      dist = d;
      l = id;
    }
  }
  for (int i = 0; i < v[id].size(); ++i) {
    if (!visited[v[id][i]]) {
      dfs(v[id][i], d + 1);
    }
  }
}
bool f(int id, int d) {
  visited[id] = 1;
  if (d == dist) {
    h.push_back(id);
    return 1;
  }
  for (int i = 0; i < v[id].size(); ++i) {
    if (!visited[v[id][i]]) {
      if (f(v[id][i], d + 1)) {
        h.push_back(id);
        return 1;
      }
    }
  }
  return 0;
}
void dd(int id, int d) {
  visited[id] = 1;
  if (v[id].size() == 1) {
    s.insert(d);
  }
  for (int i = 0; i < v[id].size(); ++i) {
    if (!visited[v[id][i]]) {
      dd(v[id][i], d + 1);
    }
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; ++i) {
    int x, y;
    cin >> x >> y;
    v[x].push_back(y);
    v[y].push_back(x);
  }
  dfs(1, 0);
  for (int i = 0; i < n; ++i) visited[i + 1] = 0;
  dfs(l, 0);
  for (int i = 0; i < n; ++i) visited[i + 1] = 0;
  if (dist % 2 == 0) {
    f(l, 0);
    l = h[dist / 2];
    for (int i = 0; i < n; ++i) visited[i + 1] = 0;
    dd(l, 0);
    set<int>::iterator it;
    if (s.size() == 2) {
      it = s.begin();
      int y = *it;
      it++;
      y += *it;
      while (y % 2 == 0) y /= 2;
      cout << y << endl;
      return 0;
      ;
    } else if (s.size() == 1) {
      it = s.begin();
      int y = *it;
      while (y % 2 == 0) y /= 2;
      cout << y << endl;
      return 0;
      ;
    } else {
      cout << -1 << endl;
      return 0;
      ;
    }
  } else {
    f(l, 0);
    for (int i = 0; i < h.size(); ++i) {
      if (v[h[i]].size() >= 3) {
        for (int i = 0; i < n; ++i) visited[i + 1] = 0;
        dd(h[i], 0);
        if (s.size() == 2) {
          cout << dist << endl;
          return 0;
          ;
        }
        cout << -1 << endl;
        return 0;
        ;
      }
    }
    cout << dist << endl;
    return 0;
    ;
  }
  return 0;
}
