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 = 200005;
int n;
vector<int> e[maxn];
int f[maxn][2][2];
void pd(int x, int y, int val) {
  if (f[x][y][0] == -1) return;
  if (f[x][y][0] == 0 || f[x][y][0] == val) {
    f[x][y][0] = val;
    return;
  }
  if (f[x][y][1] == 0 || f[x][y][1] == val) {
    f[x][y][1] = val;
    return;
  }
  f[x][y][0] = -1;
}
void dfs(int u, int fa) {
  for (int i = 0; i < e[u].size(); i++) {
    int v = e[u][i];
    if (v == fa) continue;
    dfs(v, u);
    if (f[v][0][0] == -1 || (f[v][0][0] && f[v][0][1])) {
      f[u][0][0] = -1;
    } else {
      pd(u, 0, f[v][0][0] + 1);
    }
  }
}
void dfs2(int u, int fa) {
  bool sign = 0;
  if (f[u][1][0] == -1 || (f[u][1][0] && f[u][1][1])) sign = 1;
  int cnt = 0;
  vector<pair<int, int>> vec;
  vector<int> sp;
  for (int i = 0; i < e[u].size(); i++) {
    int v = e[u][i];
    if (v == fa) continue;
    if (f[v][0][0] == -1) {
      sp.push_back(v);
    } else {
      vec.push_back(make_pair(f[v][0][0] + 2, v));
      if (f[v][0][1]) {
        vec.push_back(make_pair(f[v][0][1] + 2, v));
        sp.push_back(v);
      }
    }
    cnt++;
  }
  if (sign) {
    for (int i = 0; i < e[u].size(); i++) {
      int v = e[u][i];
      if (v == fa) continue;
      f[v][1][0] = -1;
      dfs2(v, u);
    }
    return;
  }
  if (!f[u][1][0]) {
    if (cnt == 1) vec.push_back(make_pair(1, u));
  } else {
    vec.push_back(make_pair(f[u][1][0] + 1, u));
  }
  vector<pair<int, int>> cvec;
  sort(vec.begin(), vec.end());
  for (int i = 0; i < vec.size(); i++) {
    int pos = i;
    for (int j = i; j < vec.size(); j++) {
      if (vec[j].first != vec[i].first) break;
      pos = j;
    }
    cvec.push_back(vec[i]);
    if (pos > i) cvec.push_back(vec[i + 1]);
    i = pos;
  }
  for (int i = 0; i < e[u].size(); i++) {
    int v = e[u][i];
    if (v == fa) continue;
    for (int j = 0; j < sp.size(); j++) {
      if (sp[j] != v) {
        f[v][1][0] = -1;
        break;
      }
    }
    for (int j = 0; j < cvec.size(); j++) {
      pair<int, int> pr = cvec[j];
      if (pr.second == v) continue;
      pd(v, 1, pr.first);
      if (f[v][1][0] == -1) break;
    }
  }
  for (int i = 0; i < e[u].size(); i++) {
    int v = e[u][i];
    if (v == fa) continue;
    dfs2(v, u);
  }
}
int main() {
  cin >> n;
  for (int i = 1; i < n; i++) {
    int u, v;
    cin >> u >> v;
    e[u].push_back(v);
    e[v].push_back(u);
  }
  dfs(1, 0);
  dfs2(1, 0);
  int ret = -1;
  for (int i = 1; i <= n; i++) {
    if (f[i][0][0] == -1 || f[i][1][0] == -1 || (f[i][1][0] && f[i][1][1]))
      continue;
    vector<int> v;
    if (f[i][0][0]) {
      v.push_back(f[i][0][0]);
      if (f[i][0][1]) v.push_back(f[i][0][1]);
    }
    if (f[i][1][0]) {
      v.push_back(f[i][1][0]);
      if (f[i][1][1]) v.push_back(f[i][1][1]);
    }
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    if (v.size() > 2) continue;
    int sum = 0;
    for (int j = 0; j < v.size(); j++) sum += v[j];
    while (sum % 2 == 0) sum /= 2;
    if (ret == -1 || ret > sum) ret = sum;
  }
  cout << ret << endl;
  return 0;
}
