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;
using ld = long double;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using mii = map<int, int>;
using ii = pair<int, int>;
using vii = vector<ii>;
using msi = map<string, int>;
using vvii = vector<vii>;
using vmii = vector<mii>;
vvi G;
vmii H;
vvi cues;
void dfs(int u, int p = -1, int l = 0, int nod = -1) {
  if (G[u].size() == 1) {
    cues[nod].push_back(l);
  } else if (G[u].size() == 2) {
    for (int v : G[u])
      if (v != p) {
        dfs(v, u, l + 1, nod);
      }
  } else {
    if (nod != -1) {
      H[u][nod] = l;
      H[nod][u] = l;
    }
    for (int v : G[u])
      if (v != p) {
        dfs(v, u, 1, u);
      }
  }
}
int pot2(int l) {
  while (l % 2 == 0) l /= 2;
  return l;
}
int main() {
  int n;
  cin >> n;
  G = vvi(n);
  for (int i = 0; i < n - 1; ++i) {
    int u, v;
    cin >> u >> v;
    --u;
    --v;
    G[u].push_back(v);
    G[v].push_back(u);
  }
  int root = -1;
  for (int i = 0; i < n; ++i)
    if (G[i].size() > 2) root = i;
  if (root == -1) {
    cout << pot2(n - 1) << endl;
    return 0;
  }
  cues = vvi(n);
  H = vmii(n);
  dfs(root);
  queue<int> q;
  for (int i = 0; i < n; ++i) {
    if (H[i].size() == 1) q.push(i);
  }
  int fi = -1;
  if (H[root].size() == 0) fi = root;
  int buc = 0;
  while (not q.empty()) {
    if (++buc > 2 * n + 10) {
      cout << -1 << endl;
      return 0;
    }
    int u = q.front();
    q.pop();
    sort(cues[u].begin(), cues[u].end());
    cues[u].resize(unique(cues[u].begin(), cues[u].end()) - cues[u].begin());
    if (cues[u].size() >= 3) {
      cout << -1 << endl;
      return 0;
    }
    if (cues[u].size() == 2) {
      q.push(u);
    }
    if (cues[u].size() == 1 and H[u].size() == 1) {
      int v = H[u].begin()->first;
      int l = H[u].begin()->second;
      H[u].clear();
      H[v].erase(u);
      cues[v].emplace_back(cues[u][0] + l);
      cues[u].clear();
      if (H[v].size() == 0) {
        fi = v;
        break;
      }
      if (H[v].size() == 1) q.push(v);
    }
  }
  if (fi == -1) {
    cout << -1 << endl;
  } else {
    sort(cues[fi].begin(), cues[fi].end());
    cues[fi].resize(unique(cues[fi].begin(), cues[fi].end()) -
                    cues[fi].begin());
    if (cues[fi].size() >= 3) {
      cout << -1 << endl;
      return 0;
    }
    int l = 0;
    for (int c : cues[fi]) l += c;
    cout << pot2(l) << endl;
  }
}
