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 + 7;
set<int> se[N];
vector<int> G[N];
queue<int> que;
int d[N], vis[N];
int n;
int bfs() {
  while (!que.empty()) {
    int u = que.front();
    que.pop();
    vis[u] = 1;
    for (int i = 0; i < (int)G[u].size(); i++) {
      int v = G[u][i];
      if (vis[v]) continue;
      se[v].insert(*se[u].begin() + 1);
      d[v]--;
      if (d[v] == 1 && se[v].size() == 1) que.push(v);
    }
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    if (se[i].size() > 2) return -1;
    if (ans != 0 && se[i].size() == 2) return -1;
    if (se[i].size() == 2) {
      for (auto h : se[i]) ans += h;
    }
  }
  if (ans == 0) {
    for (int i = 1; i <= n; i++) ans = max(ans, *se[i].begin());
    ans = ans * 2;
  }
  while (ans % 2 == 0 && ans > 0) ans /= 2;
  return ans;
}
int main() {
  scanf("%d", &n);
  for (int i = 0, u, v; i < n - 1; i++) {
    scanf("%d %d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  for (int i = 1; i <= n; i++) {
    d[i] = G[i].size();
    if (d[i] == 1) {
      que.push(i);
      se[i].insert(0);
    }
  }
  memset(vis, 0, sizeof(vis));
  printf("%d\n", bfs());
  return 0;
}
