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;
vector<long long> adj[1000000];
long long par[1000000], ast, a1, a2;
bool vis[1000000];
void dfs1(long long i) {
  vis[i] = 1;
  for (int j = 0; j < adj[i].size(); j++) {
    if (vis[adj[i][j]] == 0) {
      par[adj[i][j]] = i;
      dfs1(adj[i][j]);
    }
  }
}
long long dfs2(long long i) {
  set<long long> st;
  if (vis[i]) return 0;
  vis[i] = 1;
  for (int j = 0; j < adj[i].size(); j++) {
    if (vis[adj[i][j]] == 0) {
      long long temp = dfs2(adj[i][j]);
      st.insert(temp + 1);
    }
  }
  if (st.size() == 0) st.insert(0);
  set<long long>::iterator itr = st.begin();
  if (st.size() == 2) {
    if (ast == 0) {
      ast = i;
      a1 = *itr;
      itr++;
      a2 = *itr;
      itr--;
    }
  }
  if (st.size() > 2) {
    if (ast == 0) ast = -1;
  }
  return *itr;
}
int main() {
  long long n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    long long a, b;
    cin >> a >> b;
    adj[a].push_back(b);
    adj[b].push_back(a);
  }
  dfs1(1);
  memset(vis, 0, sizeof(vis));
  long long ans = dfs2(1);
  if (ast == -1)
    cout << ast;
  else if (ast == 0) {
    while (ans % 2 == 0) ans /= 2;
    cout << ans;
  } else {
    memset(vis, 0, sizeof(vis));
    vis[ast] = 1;
    long long df = ast;
    if (ast == 1) {
      ans = a1 + a2;
      while (ans % 2 == 0) ans /= 2;
      cout << ans;
      return 0;
    }
    ast = 0;
    long long temp = dfs2(par[df]) + 1;
    if (ast == 0 && (temp == a1 || temp == a2)) {
      if (a1 != a2)
        ans = a1 + a2;
      else
        ans = a1;
      while (ans % 2 == 0) ans /= 2;
      cout << ans;
    } else
      cout << "-1";
  }
  return 0;
}
