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;
vector<int> V[1000005];
int deg[1000005];
int col;
int sz[1000005];
void dfs(int n, int p) {
  if (V[n].size() == 1 && p != -1) {
    sz[n] = 1;
    return;
  }
  set<int> S;
  for (int i = 0; i < V[n].size(); ++i) {
    if (V[n][i] == p) continue;
    dfs(V[n][i], n);
    S.insert(sz[V[n][i]]);
  }
  if (S.size() > 1 || *(S.begin()) == -1) {
    sz[n] = -1;
  }
  sz[n] = 1 + *(S.begin());
}
int ans;
void sdfs(int n, int p, int val = 0) {
  set<int> S;
  map<int, int> M;
  if (val) {
    S.insert(val);
  }
  for (int i = 0; i < V[n].size(); ++i) {
    if (V[n][i] == p) continue;
    S.insert(sz[V[n][i]]);
    ++M[sz[V[n][i]]];
  }
  if (S.size() <= 2) {
    int u = *S.begin();
    if (S.size() == 2) {
      auto it = S.begin();
      ++it;
      u += (*it);
    }
    if (ans == -1)
      ans = u;
    else
      ans = min(ans, u);
  }
  for (int i = 0; i < V[n].size(); ++i) {
    if (V[n][i] == p) continue;
    --M[sz[V[n][i]]];
    if (M[sz[V[n][i]]] == 0) {
      S.erase(sz[V[n][i]]);
    }
    if (S.size() == 1) {
      sdfs(V[n][i], n, *(S.begin()) + 1);
    }
    ++M[sz[V[n][i]]];
    S.insert(sz[V[n][i]]);
  }
}
int main() {
  int n;
  cin >> n;
  col = 1;
  ans = -1;
  for (int i = 1; i < n; ++i) {
    int a, b;
    scanf("%d %d", &a, &b);
    ++deg[a];
    ++deg[b];
    V[a].push_back(b);
    V[b].push_back(a);
  }
  int one = 0;
  int two = 0;
  for (int i = 1; i <= n; ++i) {
    if (deg[i] == 1)
      ++one;
    else if (deg[i] == 2)
      ++two;
  }
  if (one == 2 && two == n - 2) {
    while (n % 2) {
      n = (n + 1) / 2;
    }
    cout << n << endl;
    return 0;
  }
  int ind = 0;
  for (int i = 1; i <= n; ++i) {
    if (deg[i] >= 3) {
      ind = i;
      break;
    }
  }
  dfs(ind, -1);
  sdfs(ind, -1);
  cout << ans << endl;
  return 0;
}
