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 maxn = 2e5 + 10;
vector<int> g[maxn];
int dw[maxn], up[maxn], fa[maxn];
void dfs1(int u, int f) {
  int le = 0;
  fa[u] = f;
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == f) continue;
    dfs1(v, u);
    if (dw[v] == -1)
      le = -1;
    else {
      if (le == 0) le = dw[v];
      if (le != dw[v]) le = -1;
    }
  }
  if (le == -1)
    dw[u] = -1;
  else
    dw[u] = le + 1;
}
void dfs2(int u, int f, int le) {
  up[u] = le;
  map<int, int> mp;
  if (le) ++mp[le];
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == f) continue;
    ++mp[dw[v]];
  }
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == f) continue;
    --mp[dw[v]];
    if (mp[dw[v]] == 0) mp.erase(dw[v]);
    int l = 0;
    if (mp.size() == 1 && (mp.begin()->first) >= 0)
      l = (mp.begin()->first) + 1;
    else if (mp.size() == 0)
      l = le + 1;
    else
      l = -1;
    dfs2(v, u, l);
    ++mp[dw[v]];
  }
}
int fun(int a) {
  while (a % 2) {
    a = a / 2 + 1;
  }
  return a;
}
int main() {
  int n;
  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);
  }
  dfs1(1, 0);
  dfs2(1, 0, 0);
  int ans = maxn;
  set<int> ss;
  for (int u = 1; u <= n; u++) {
    ss.clear();
    if (up[u]) ss.insert(up[u]);
    for (int i = 0; i < g[u].size(); i++)
      if (g[u][i] != fa[u]) ss.insert(dw[g[u][i]]);
    if (ss.size() == 1 && (*ss.begin()) >= 0)
      ans = min(ans, fun((*ss.begin()) + 1));
    if (ss.size() == 2) {
      auto it = ss.begin();
      int tot = 0;
      int a = *it, b = *(++it);
      if (a >= 0 && b >= 0) ans = min(ans, fun(a + b + 1));
    }
  }
  if (ans == maxn) ans = 0;
  printf("%d\n", ans - 1);
  return 0;
}
