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<int> h;
vector<vector<int>> tree;
int best = 1e9;
int dfs(int x, int par) {
  if (tree[x].size() == 1 and tree[x][0] == par) return h[x] = 1;
  int he = -2;
  for (int i = 0; i < tree[x].size(); ++i) {
    if (tree[x][i] != par) {
      if (he == -2)
        he = dfs(tree[x][i], x);
      else if (he != dfs(tree[x][i], x))
        he = -1;
    }
  }
  if (he != -1) ++he;
  return h[x] = he;
}
void dfs2(int x, int par) {
  map<int, int> hs;
  int one = -1;
  vector<vector<int>> &g = tree;
  for (int i = 0; i < g[x].size(); ++i) {
    ++hs[h[g[x][i]]];
  }
  int first = hs.begin()->first, second = 0;
  if (hs.size() == 2) second = (++hs.begin())->first;
  if (hs.size() <= 2 and first != -1) {
    int cand = first + second + 1;
    while (cand & 1) {
      cand = 1 + cand >> 1;
    }
    best = min(best, cand);
  }
  for (int i = 0; i < g[x].size(); ++i) {
    if (g[x][i] != par) {
      if (hs.size() == 1 and hs[-1] == 0) {
        ++h[x];
        dfs2(g[x][i], x);
        --h[x];
      } else if (hs.size() == 1 and hs[-1] == 1) {
        h[x] = 1;
        dfs2(g[x][i], x);
        h[x] = -1;
      } else if (hs.size() == 2 and hs[first] == 1 and first == h[g[x][i]] and
                 second != -1) {
        h[x] = second + 1;
        dfs2(g[x][i], x);
        h[x] = -1;
      } else if (hs.size() == 2 and hs[second] == 1 and second == h[g[x][i]] and
                 first != -1) {
        h[x] = first + 1;
        dfs2(g[x][i], x);
        h[x] = -1;
      }
    }
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  tree = vector<vector<int>>(n);
  h = vector<int>(n, -1);
  for (int i = 0; i < n - 1; ++i) {
    int u, v;
    cin >> u >> v;
    --u;
    --v;
    tree[u].push_back(v);
    tree[v].push_back(u);
  }
  dfs(0, -1);
  dfs2(0, -1);
  if (best == 1e9)
    cout << -1 << '\n';
  else
    cout << best - 1 << '\n';
}
