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;
int n;
vector<int> g[200010];
bool vis[200010];
int deg[200010];
set<int> st[200010];
int main() {
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int x, y;
    cin >> x >> y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  queue<pair<int, int> > q;
  for (int i = 0; i < n; i++) {
    deg[i + 1] = g[i + 1].size();
    if (g[i + 1].size() == 1) q.push(make_pair(i + 1, 0));
  }
  int last = -1;
  int c = 0;
  while (q.size()) {
    c++;
    int p = q.front().first, x = q.front().second;
    q.pop();
    last = p;
    vis[p] = 1;
    for (int i = 0; i < g[p].size(); i++) deg[g[p][i]]--;
    for (int i = 0; i < g[p].size(); i++) {
      int fa = g[p][i];
      if (!vis[fa]) {
        st[fa].insert(x + 1);
        if (deg[fa] == 1 && st[fa].size() == 1) q.push(make_pair(fa, x + 1));
      }
    }
  }
  if (c < n - 1)
    cout << "-1";
  else {
    if (c == n - 1)
      for (int i = 0; i < n; i++)
        if (!vis[i + 1]) last = i + 1;
    if (st[last].size() > 2) {
      cout << -1;
      return 0;
    }
    int x = 0;
    for (set<int>::iterator it = st[last].begin(); it != st[last].end(); it++)
      x += *it;
    while (x % 2 == 0) x >>= 1;
    cout << x;
  }
  return 0;
}
