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> g[maxn];
int n, vis[maxn], d[maxn];
set<int> S[maxn];
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
    d[a]++;
    d[b]++;
  }
  queue<int> Q;
  for (int i = 1; i <= n; i++) {
    if (g[i].size() == 1) {
      Q.push(i);
      S[i].insert(0);
    }
  }
  while (!Q.empty()) {
    int now = Q.front();
    vis[now] = 1;
    Q.pop();
    for (int i = 0; i < g[now].size(); i++) {
      int v = g[now][i];
      if (vis[v]) continue;
      S[v].insert((*S[now].begin()) + 1);
      d[v]--;
      if (d[v] == 1 && S[v].size() == 1) {
        Q.push(v);
      }
    }
  }
  int ans = 0, num2 = 0;
  for (int i = 1; i <= n; i++) {
    if (S[i].size() == 0) {
      cout << "-1" << endl;
      return 0;
    }
    if (S[i].size() > 2) {
      cout << "-1" << endl;
      return 0;
    }
    if (S[i].size() == 1) {
      ans = max(ans, *S[i].begin());
    }
    if (S[i].size() == 2) {
      ans = max(ans, *S[i].begin() + *S[i].rbegin());
      num2++;
    }
  }
  if (num2 > 1) {
    cout << "-1" << endl;
    return 0;
  }
  while (ans % 2 == 0) {
    ans /= 2;
  }
  cout << ans << endl;
}
