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 nmax = 2 * 1e5 + 5;
int n;
vector<int> gf[nmax];
int viz[nmax];
int lung[nmax];
int nivel[nmax];
int t[nmax];
bool dfs(int node, int root) {
  viz[node] = 1;
  int last = -1;
  bool checkCurr = true;
  lung[node] = 1;
  for (int i = 0; i < gf[node].size(); ++i) {
    int vc = gf[node][i];
    if (viz[vc] == 0) {
      checkCurr &= dfs(vc, root);
      if (checkCurr == false) {
        break;
      }
      if (node == root) {
        continue;
      }
      if (last == -1) {
        last = lung[vc];
        lung[node] += lung[vc];
      } else if (last != lung[vc]) {
        return false;
      }
    }
  }
  return checkCurr;
}
void diametru(int node) {
  viz[node] = 1;
  for (int i = 0; i < gf[node].size(); ++i) {
    int vc = gf[node][i];
    if (viz[vc] == 0) {
      nivel[vc] = nivel[node] + 1;
      t[vc] = node;
      diametru(vc);
    }
  }
}
pair<int, int> getDiameter() {
  nivel[1] = 1;
  diametru(1);
  pair<int, int> ans = make_pair(-1, -1);
  for (int i = 1; i <= n; ++i) {
    if (nivel[i] > ans.second) {
      ans = make_pair(i, nivel[i]);
    }
    nivel[i] = 0;
    viz[i] = 0;
    t[i] = 0;
  }
  assert(ans.first != -1);
  nivel[ans.first] = 1;
  diametru(ans.first);
  for (int i = 1; i <= n; ++i) {
    if (nivel[i] >= ans.second) {
      ans = make_pair(i, nivel[i]);
    }
    viz[i] = 0;
  }
  int node = ans.first;
  int cuCat = ans.second / 2 + 1;
  while (node != 0) {
    if (nivel[node] == cuCat) {
      ans = make_pair(node, ans.second);
      break;
    }
    node = t[node];
    if (node == 0) {
      assert(false);
    }
  }
  return ans;
}
int main() {
  ios::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i < n; ++i) {
    int x, y;
    cin >> x >> y;
    gf[x].push_back(y);
    gf[y].push_back(x);
  }
  int ans = (1 << 30);
  pair<int, int> diametruPair = getDiameter();
  bool pot = dfs(diametruPair.first, diametruPair.first);
  if (!pot) {
    cout << -1 << "\n";
    return 0;
  }
  set<int> mySet;
  int root = diametruPair.first;
  for (int i = 0; i < gf[root].size(); ++i) {
    int vc = gf[root][i];
    mySet.insert(lung[vc]);
  }
  if (mySet.size() > 2) {
    cout << -1 << "\n";
    return 0;
  } else {
    ans = 1;
    for (auto x : mySet) {
      ans += x;
    }
  }
  while (ans > 1 && ans % 2 == 1) {
    ans = ans / 2 + 1;
  }
  ans--;
  cout << ans << "\n";
  return 0;
}
