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;
set<int> g[1000005], d[1000005];
queue<int> q;
int vis[1000005];
int solve(int n) {
  int res = -1;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    if (vis[u]) continue;
    if (g[u].size() == 0) {
      res = *d[u].begin() + *d[u].rbegin();
      break;
    } else if (g[u].size() == 1) {
      if (d[u].size() == 1) {
        vis[u] = 1;
        int v = *g[u].begin();
        g[u].erase(v);
        g[v].erase(u);
        q.push(v);
        d[v].insert(*d[u].begin() + 1);
        if (d[v].size() > 2) return -1;
      }
    }
  }
  return res;
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    g[u].insert(v);
    g[v].insert(u);
  }
  for (int i = 1; i <= n; i++) {
    if (g[i].size() == 1) {
      q.push(i);
      d[i].insert(0);
    }
  }
  int ans = solve(n);
  while (ans % 2 == 0) ans /= 2;
  printf("%d\n", ans);
}
