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>
#pragma comment(linker, "/STACK:1024000000,1024000000")
using namespace std;
const double eps = 1e-6;
const double PI = acos(-1.);
const double E = 2.71828182845904523536;
const int MOD = (int)1e9 + 7;
const int INF = 0x3f3f3f3f;
const long long INFLL = 0x7f7f7f7f;
const int N = 1e5 + 7;
const int M = 2000000 + 5;
inline int popcnt(int x) { return __builtin_popcount(x); }
inline int clz(int x) { return __builtin_clz(x); }
inline int clz(long long x) { return __builtin_clzll(x); }
inline int lg2(int x) { return !x ? -1 : 31 - clz(x); }
inline int lg2(long long x) { return !x ? -1 : 63 - clz(x); }
int n, ms, md, ms2, md2, vis[222222], o;
vector<int> g[222222];
void dfs1(int u, int p, int d) {
  if (d > md) md = d, ms = u;
  for (int v : g[u])
    if (p != v) {
      dfs1(v, u, d + 1);
    }
}
void dfs2(int u, int p, int d) {
  if (d > md2) md2 = d, ms2 = u;
  for (int v : g[u])
    if (p != v) {
      dfs2(v, u, d + 1);
    }
}
void dfs(int u, int d, int p) {
  vis[u]++;
  if (d == md2 / 2) return;
  for (int v : g[u])
    if (v != p) dfs(v, d + 1, u);
}
pair<int, int> mydfs(int o, int p) {
  if (g[o].size() == 1) return make_pair(1, -1);
  vector<int> vec;
  for (int v : g[o])
    if (v != p) {
      pair<int, int> pi = mydfs(v, o);
      if (pi.first == -1) return make_pair(-1, -1);
      vec.push_back(pi.first + 1);
      if (pi.second != -1) vec.push_back(pi.second + 1);
    }
  sort(vec.begin(), vec.end());
  vec.erase(unique(vec.begin(), vec.end()), vec.end());
  map<int, int> mp;
  for (int cp : vec) {
    mp[cp]++;
  }
  if (mp.size() > 2)
    return make_pair(-1, -1);
  else if (mp.size() == 2)
    return make_pair(vec[0], vec[vec.size() - 1]);
  else
    return make_pair(vec[0], -1);
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    g[u].push_back(v);
    g[v].push_back(u);
  }
  if (n == 1 || n == 2)
    return 0 * printf("%d\n", n - 1);
  else if (n == 3)
    return 0 * puts("1");
  md = 0, ms = -1;
  md2 = 0;
  dfs1(1, -1, 1);
  dfs2(ms, -1, 1);
  dfs(ms, 0, -1);
  dfs(ms2, 0, -1);
  for (int i = 1; i <= n; i++) {
    if (vis[i] == 2) {
      o = i;
      break;
    }
  }
  pair<int, int> ret = mydfs(o, -1);
  if (ret.first == -1) return 0 * puts("-1");
  int tret;
  if (ret.second == -1)
    tret = ret.first - 1;
  else
    tret = (ret.first + ret.second) - 2;
  while (tret % 2 == 0) tret /= 2;
  cout << tret << endl;
  return 0;
}
