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;
void rf() {}
const int nx[8] = {2, -2, -2, 2, 1, 1, -1, -1};
const int ny[8] = {1, 1, -1, -1, 2, -2, -2, 2};
const int Nx[4] = {0, 0, -1, 1};
const int Ny[4] = {1, -1, 0, 0};
const long long LINF = (long long)5e18;
const int INF = 1e9 + 7;
const int N = 2e5 + 10;
const int MAXN = 1e6 + 50;
const double EPS = 1e-9, PI = 3.14159265359;
inline int get_int() {
  char x = getchar();
  int ret = 0;
  bool neg = 0;
  while (!('0' <= x && x <= '9')) {
    if (x == '-') neg = 1;
    x = getchar();
  }
  while ('0' <= x && x <= '9') {
    ret = ret * 10 + x - '0';
    x = getchar();
  }
  if (neg) ret *= -1;
  return ret;
}
int n;
int root;
int dep[N];
bool boo[N];
vector<int> v[N];
void pre_dfs(int x, int p = -1) {
  boo[x] = 1;
  int clr = -1;
  for (auto it : v[x]) {
    if (it == p) continue;
    pre_dfs(it, x);
    dep[x] = max(dep[x], dep[it] + 1);
    boo[x] &= boo[it];
    if (clr != -1 && dep[it] != clr) boo[x] = 0;
    clr = dep[it];
  }
}
void add_one(set<int> &second) {
  set<int> go;
  for (auto it : second) go.insert(it + 1);
  second = go;
}
int ans = INF;
void dfs1(int x, int p = -1, set<int> up = {}) {
  vector<int> g;
  for (auto it : v[x]) {
    if (it == p) continue;
    g.push_back(it);
  }
  set<int> cur;
  map<int, int> cnt;
  bool ok = 1;
  for (auto it : g) {
    if (!boo[it]) {
      ok = 0;
    }
    cnt[dep[it]]++;
    cur.insert(dep[it]);
  }
  if (ok && int(cur.size()) <= 2) {
    set<int> ss = cur;
    for (auto it : up) ss.insert(it);
    if (int(ss.size()) <= 2) {
      int cur_sum = 0;
      for (auto it : ss) cur_sum += it;
      ans = min(ans, cur_sum + int(ss.size()));
    }
  }
  if (int(cur.size()) <= 3) {
    int r = int(g.size());
    for (int i = int(g.size()) - 1; i >= 0; i--) {
      if (!boo[g[i]]) break;
      r = i;
    }
    ok = 1;
    for (int i = 0; i < int(g.size()); i++) {
      int it = g[i];
      if (ok && i + 1 >= r) {
        set<int> go = cur;
        if (cnt[dep[it]] == 1) go.erase(dep[it]);
        for (auto j : up) go.insert(j);
        if (int(go.size()) < 2) {
          add_one(go);
          dfs1(it, x, go);
        }
      }
      ok &= boo[it];
    }
  }
}
int main() {
  srand(time(0));
  rf();
  cin >> n;
  for (int i = 1; i < n; i++) {
    int x, y;
    cin >> x >> y;
    v[x].push_back(y);
    v[y].push_back(x);
  }
  for (int i = 1; i <= n; i++)
    if (int(v[i].size()) > 1) root = i;
  pre_dfs(root);
  dfs1(root);
  if (ans == INF) ans = -1;
  cout << ans;
  return 0;
}
