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<vector<int> > G;
vector<int> M;
vector<int> m;
int inf1 = 1e6;
void dfs(int x, int p) {
  m[x] = inf1;
  M[x] = 0;
  for (int i = 0; i < (int)G[x].size(); ++i) {
    int y = G[x][i];
    if (y == p) continue;
    dfs(y, x);
    m[x] = min(m[x], m[y] + 1);
    M[x] = max(M[x], M[y] + 1);
  }
  if (m[x] == inf1) m[x] = 0;
}
int res;
void dfs2(int x, int p, int d) {
  int mid = (int)G[x].size() + 1;
  int M1[mid];
  int m1[mid];
  int t = 0;
  for (int i = 0; i < (int)G[x].size(); ++i) {
    int y = G[x][i];
    if (y == p) continue;
    M1[t] = M[y] + 1;
    m1[t] = m[y] + 1;
    if (t != 0) {
      M1[t] = max(M1[t - 1], M1[t]);
      m1[t] = min(m1[t - 1], m1[t]);
    }
    ++t;
  }
  int M2[mid];
  int m2[mid];
  mid -= 3;
  if (x == 0) ++mid;
  t = mid;
  for (int i = (int)G[x].size() - 1; i >= 0; --i) {
    int y = G[x][i];
    if (y == p) continue;
    M2[t] = M[y] + 1;
    m2[t] = m[y] + 1;
    if (t != mid) {
      M2[t] = max(M2[t + 1], M2[t]);
      m2[t] = min(m2[t + 1], m2[t]);
    }
    --t;
  }
  if (mid < 0)
    res = min(d, res);
  else if (M1[mid] == m1[mid]) {
    if (d == 0 or d == M1[mid]) res = min(M1[mid], res);
  }
  t = 0;
  for (int i = 0; i < (int)G[x].size(); ++i) {
    int y = G[x][i];
    if (y == p) continue;
    int tt1 = -2, tt2 = -3;
    if (t == 0)
      tt1 = -1;
    else if (M1[t - 1] == m1[t - 1])
      tt1 = m1[t - 1];
    if (t == mid)
      tt2 = -1;
    else if (M2[t + 1] == m2[t + 1])
      tt2 = m2[t + 1];
    if (tt1 == tt2 or (tt1 == -1 and tt2 != -3) or (tt1 != -2 and tt2 == -1)) {
      int kk = tt1;
      if (kk == -1) kk = tt2;
      if (d == 0 or kk == -1 or kk == d) {
        int rr = max(kk, d);
        dfs2(y, x, rr + 1);
      }
    }
    ++t;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  G = vector<vector<int> >(n);
  M = m = vector<int>(n);
  for (int i = 0; i < n - 1; ++i) {
    int x, y;
    cin >> x >> y;
    --x;
    --y;
    G[x].push_back(y);
    G[y].push_back(x);
  }
  dfs(0, -1);
  res = inf1;
  dfs2(0, -1, 0);
  if (res == inf1)
    cout << -1 << endl;
  else
    cout << res << endl;
}
