#include <bits/stdc++.h>
using namespace std;
const int max_n = 202222, inf = 1011111111;
int n, was, sz[max_n], p[max_n];
queue<int> q;
vector<int> g[max_n], all[max_n];
void dfs(int v, int pp) {
  p[v] = pp;
  for (int i = 0; i < g[v].size(); ++i) {
    if (g[v][i] != pp) {
      ++sz[v];
      dfs(g[v][i], v);
    }
  }
  if (sz[v] == 0) {
    q.push(v);
    all[v].push_back(0);
  }
}
int proc(int root) {
  while (!q.empty()) {
    q.pop();
  }
  for (int i = 1; i <= n; ++i) {
    sz[i] = 0;
    all[i].clear();
  }
  dfs(root, -1);
  int last = 0;
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    sort(all[v].begin(), all[v].end());
    all[v].erase(unique(all[v].begin(), all[v].end()), all[v].end());
    if (all[v].size() == 2) {
      while (all[v].size() == 2 && all[v][0] % 2 == all[v][1] % 2) {
        int len = (all[v][1] - all[v][0]) / 2;
        all[v].pop_back();
        if (len) {
          all[v].push_back(len);
        }
      }
    }
    if (v == root && all[v].size() == 2) {
      return all[v][0] + all[v][1];
    }
    if (all[v].size() > 2 || all[v].size() == 2) {
      if (was) {
        printf("-1\n");
        exit(0);
      }
      was = 1;
      return proc(v);
    }
    if (v == root) {
      return all[v][0];
    }
    --sz[p[v]];
    if (sz[p[v]] == 0) {
      q.push(p[v]);
    }
    all[p[v]].push_back(all[v][0] + 1);
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    g[u].push_back(v);
    g[v].push_back(u);
  }
  int ans = proc(1);
  while (ans % 2 == 0) {
    ans /= 2;
  }
  printf("%d\n", ans);
  return 0;
}
