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 INF = 1E9 + 10;
const int N = 2E5 + 10;
map<int, int> state[N];
int n, f[N], g[N];
vector<int> G[N];
void dfs1(int u, int fa) {
  state[u].clear();
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    dfs1(v, u);
    state[u][f[v]]++;
  }
  if (state[u].size() >= 2 || state[u].begin()->first == -1) {
    f[u] = -1;
  } else {
    if (state[u].size() == 1)
      f[u] = state[u].begin()->first + 1;
    else
      f[u] = 0;
  }
}
void dfs2(int u, int fa) {
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    map<int, int> make_pair = state[u];
    if (make_pair.size() > 2 || g[u] == -1) {
      g[v] = -1;
      continue;
    }
    make_pair[f[v]]--;
    int cnt = 0, val = 0;
    for (map<int, int>::iterator it = make_pair.begin(); it != make_pair.end();
         it++) {
      if (it->second == 0) {
        continue;
      } else {
        cnt++;
        val = it->first;
      }
    }
    if (cnt == 1 && val != -1) {
      if (g[u] == 0 || g[u] == val + 1) {
        g[v] = val + 2;
      } else {
        g[v] = -1;
      }
    } else if (cnt == 0) {
      g[v] = g[u] + 1;
    } else {
      g[v] = -1;
    }
  }
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    dfs2(v, u);
  }
}
int gen(int u) {
  if (u == 0) return 0;
  if (u & 1)
    return u;
  else
    return gen(u / 2);
}
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);
  }
  dfs1(1, -1);
  dfs2(1, -1);
  int ans = n + 10;
  for (int i = 1; i <= n; i++) {
    if (f[i] != -1 && g[i] != -1) {
      ans = min(ans, gen(f[i] + g[i]));
    }
  }
  if (ans == n + 10)
    puts("-1");
  else
    printf("%d\n", ans);
  return 0;
}
