#include <bits/stdc++.h>
using namespace std;
class TaskE {
 public:
  int n;
  vector<vector<int>> G;
  TaskE() { std::ios::sync_with_stdio(false); }
  int hueva = -1;
  pair<bool, int> dfs(int v, int p = -1) {
    int deg = G[v].size();
    if (p != -1) --deg;
    if (deg == 0) return {true, 0};
    if (deg == 1) {
      for (int u : G[v]) {
        if (u == p) continue;
        auto ret = dfs(u, v);
        return {ret.first, ret.second + 1};
      }
      assert(false);
    }
    if (p != -1) {
      int val = -1;
      for (int u : G[v]) {
        if (u == p) continue;
        auto ret = dfs(u, v);
        if (ret.first == false) return {false, 0};
        if (val == -1) val = ret.second;
        if (val != ret.second) {
          if (hueva == -1) hueva = v;
          return {false, 0};
        }
      }
      return {true, val + 1};
    } else {
      int val0 = -1;
      int val1 = -1;
      for (int u : G[v]) {
        auto ret = dfs(u, v);
        if (ret.first == false) return {false, 0};
        if (val0 == -1) {
          val0 = ret.second;
        } else if (val0 != ret.second) {
          if (val1 == -1) {
            val1 = ret.second;
          } else if (val1 != ret.second) {
            if (hueva == -1) hueva = v;
            return {false, 0};
          }
        }
      }
      ++val0;
      if (val1 != -1) val0 += val1 + 1;
      return {true, val0};
    }
  }
  void solve(std::istream& in, std::ostream& out) {
    int m;
    in >> n;
    G.resize(n);
    for (int i = 0; i < n - 1; ++i) {
      int v, u;
      in >> v >> u;
      --v;
      --u;
      G[v].push_back(u);
      G[u].push_back(v);
    }
    int s = -1;
    for (int i = 0; i < n; ++i) {
      if (G[i].size() > 2) s = i;
    }
    pair<bool, int> ret;
    if (s == -1) {
      ret = {true, n - 1};
    } else {
      ret = dfs(s);
      if (!ret.first) {
        ret = dfs(hueva);
      }
    }
    if (!ret.first) {
      out << "-1" << endl;
    } else {
      int ans = ret.second;
      while (ans % 2 == 0) ans /= 2;
      out << ans << endl;
    }
  }
};
int main() {
  TaskE solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}
