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 N = (int)2e5 + 7;
int n;
vector<int> g[N];
int root;
bool found = false;
int len[N];
void dfs1(int v, int prev = -1) {
  if (g[v].size() == 1) return;
  vector<int> p;
  for (int to : g[v])
    if (to != prev) {
      dfs1(to, v);
      if (found) return;
      p.push_back(len[to] + 1);
    }
  sort(p.begin(), p.end());
  unique(p.begin(), p.end());
  int sz = 0;
  while (sz + 1 < p.size() && p[sz + 1] != p[sz]) sz++;
  if (sz > 1) {
    cout << -1;
    exit(0);
  }
  if (sz == 1) {
    root = v;
    found = true;
  } else
    len[v] = p[0];
}
vector<int> proot;
void dfs2(int v, int prev = -1) {
  if (g[v].size() == 1) return;
  vector<int> p;
  for (int to : g[v])
    if (to != prev) {
      dfs2(to, v);
      p.push_back(len[to] + 1);
    }
  sort(p.begin(), p.end());
  unique(p.begin(), p.end());
  if (v == root) {
    for (int i = 0; i < p.size(); i++) {
      if (i && p[i] == p[i - 1]) break;
      proot.push_back(p[i]);
    }
    return;
  }
  if (p.size() > 1) {
    cout << -1;
    exit(0);
  }
  len[v] = p[0];
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  if (n == 2) return cout << 1, 0;
  for (int i = 1; i < n; i++) {
    int u, v;
    cin >> u >> v;
    --u;
    --v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  for (int i = 0; i < n; i++)
    if (g[i].size() > 1) {
      root = i;
      break;
    }
  memset(len, 0, sizeof len);
  dfs1(root);
  memset(len, 0, sizeof len);
  dfs2(root);
  int sz = proot.size();
  if (sz > 2) return cout << -1, 0;
  int len = proot[0];
  if (sz > 1) len += proot[1];
  while (len % 2 == 0) len /= 2;
  cout << len;
}
