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 long long MOD = 1e9 + 7;
const int SIZE = 1e7 + 5;
const int INF = 1LL << 30;
const double eps = 1e-4;
const double PI = 3.1415926535897932;
vector<int> radj[200009];
vector<int> adj[200009];
int p[200009];
int v[200009];
int pv[200009];
int ans = INF;
void dfs0(int x, int pp = -1) {
  p[x] = pp;
  for (int i : radj[x]) {
    if (i == pp) continue;
    adj[x].push_back(i);
    dfs0(i, x);
  }
}
void dfs1(int x) {
  unordered_map<int, int> m;
  for (int i : adj[x]) {
    dfs1(i);
    m[v[i]]++;
  }
  if (m.find(-1) != m.end()) {
    v[x] = -1;
    return;
  }
  if (((int)(m).size()) == 0) {
    v[x] = 0;
    return;
  }
  if (((int)(m).size()) > 1) {
    v[x] = -1;
    return;
  }
  v[x] = m.begin()->first + 1;
}
void dfs2(int x) {
  map<int, int> m;
  if (x != 0) m[pv[x]] = 1;
  for (int i : adj[x]) {
    if (v[i] == -1)
      m[v[i]]++;
    else
      m[v[i] + 1]++;
  }
  if (m.find(-1) == m.end() && ((int)(m).size()) == 1) {
    int na = m.begin()->first;
    while (na % 2 == 0) na /= 2;
    ans = min(ans, na);
  }
  if (m.find(-1) == m.end() && ((int)(m).size()) == 2) {
    int na = m.begin()->first + (++m.begin())->first;
    while (na % 2 == 0) na /= 2;
    ans = min(ans, na);
  }
  for (int i : adj[x]) {
    if (v[i] == -1) {
      m[v[i]]--;
      if (m[v[i]] == 0) m.erase(v[i]);
    } else {
      m[v[i] + 1]--;
      if (m[v[i] + 1] == 0) m.erase(v[i] + 1);
    }
    if ((m.find(-1) != m.end()) || (((int)(m).size()) > 1)) {
      if (v[i] == -1)
        m[v[i]]++;
      else
        m[v[i] + 1]++;
      continue;
    }
    pv[i] = 1 + m.begin()->first;
    if (v[i] == -1)
      m[v[i]]++;
    else
      m[v[i] + 1]++;
    dfs2(i);
  }
}
int main() {
  int(n);
  scanf("%d", &n);
  for (int i = 0; i < (n - 1); ++i) {
    int a, b;
    scanf("%d%d", &a, &b);
    a--;
    b--;
    radj[a].push_back(b);
    radj[b].push_back(a);
  }
  dfs0(0);
  dfs1(0);
  dfs2(0);
  if (ans != INF)
    printf("%d", ans);
  else
    printf("-1");
}
