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;
const int N = 2e5 + 5;
const int MOD = 1e9 + 7;
const int lgn = 19;
int n, m, q;
vector<int> adj[N];
int up[N][lgn], start[N], end1[N], curr;
bool vis[N];
void dfs_lca(int node, int par) {
  start[node] = ++curr;
  up[node][0] = par;
  for (int i = 1; i < lgn; i++) {
    up[node][i] = up[up[node][i - 1]][i - 1];
  }
  int size = adj[node].size();
  for (int i = 0; i < size; i++) {
    if (par != adj[node][i] && (!vis[adj[node][i]]))
      dfs_lca(adj[node][i], node);
  }
  vis[node] = true;
  end1[node] = ++curr;
}
bool check(int u, int v) {
  return ((start[u] <= start[v]) && (end1[u] >= end1[v]));
}
int find_lca(int u, int v) {
  if (check(u, v))
    return u;
  else if (check(v, u))
    return v;
  else {
    for (int i = lgn - 1; i > -1; i--) {
      if ((up[u][i] != 0) && (!check(up[u][i], v))) u = up[u][i];
    }
  }
  return up[u][0];
}
vector<int> lvs;
int he[N];
void dfs(int v) {
  vis[v] = true;
  bool flag = true;
  for (int i = 0; i < adj[v].size(); i++)
    if (vis[adj[v][i]] == false) {
      flag = false;
      dfs(adj[v][i]);
    }
  if (flag) lvs.push_back(v);
}
void dfsh(int v, int h) {
  vis[v] = true;
  he[v] = h;
  bool flag = true;
  for (int i = 0; i < adj[v].size(); i++)
    if (vis[adj[v][i]] == false) {
      flag = false;
      dfsh(adj[v][i], h - 1);
    }
}
vector<int> roots;
int main() {
  int n, i, a, b, x, j;
  cin >> n;
  for (i = 0; i < n - 1; i++) {
    cin >> a >> b;
    adj[a].push_back(b);
    adj[b].push_back(a);
  }
  int root = -1;
  for (i = 1; i <= n; i++)
    if (adj[i].size() >= 0) {
      roots.push_back(i);
      root = 1;
    }
  int ans = -1;
  if (root == -1) {
    while (n % 2 == 1) n = (n + 1) / 2;
    cout << n - 1;
    return 0;
  } else {
    memset(vis, false, sizeof(vis));
    dfs_lca(1, 0);
    memset(vis, false, sizeof(vis));
    dfs(roots[0]);
    memset(vis, false, sizeof(vis));
    dfsh(1, 0);
    for (i = 0; i < roots.size(); i++) {
      set<int> ldis;
      for (j = 0; j < lvs.size(); j++) {
        if (lvs[j] != roots[i]) {
          x = find_lca(roots[i], lvs[j]);
          ldis.insert(2 * he[x] - he[lvs[j]] - he[roots[i]]);
          if (ldis.size() > 1) break;
        }
      }
      if (ldis.size() > 1) continue;
      ;
      if (ldis.size() == 1) ans = max(ans, *ldis.begin());
      if (ldis.size() < 1) {
        ans = max(ans, 0);
      }
    }
  }
  cout << ans;
  return 0;
}
