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 = 0x3f3f3f3f;
const int mod = 1000000007;
int head[200009], nxt[400031], vv[400031], d[200009], pre[200009];
inline void add(int u, int v) {
  static int i = 0;
  vv[i] = v;
  nxt[i] = head[u];
  head[u] = i++;
}
int bfs(int s) {
  memset(d, 0x3f, sizeof d);
  d[s] = 0;
  queue<int> q;
  q.push(s);
  int u;
  while (!q.empty()) {
    u = q.front();
    q.pop();
    for (int i = head[u]; ~i; i = nxt[i]) {
      int v = vv[i];
      if (d[v] == INF) {
        d[v] = d[u] + 1;
        pre[v] = u;
        q.push(v);
      }
    }
  }
  return u;
}
int dfs(int u, int p, int dep) {
  int ans = 0;
  for (int i = head[u]; ~i; i = nxt[i]) {
    int v = vv[i];
    if (v == p) continue;
    int temp = dfs(v, u, dep + 1);
    if (ans == 0)
      ans = temp;
    else if (ans != temp)
      return -1;
  }
  return ans ? ans : dep;
}
int main() {
  int n;
  cin >> n;
  int u, v;
  memset(head, -1, sizeof head);
  for (int i = 0; i < n - 1; ++i) {
    scanf("%d%d", &u, &v);
    add(u, v);
    add(v, u);
  }
  int u0 = bfs(1);
  int u1 = bfs(u0);
  int len = d[u1] / 2, r = u1;
  while (d[r] > len) r = pre[r];
  vector<int> ans;
  for (int i = head[r]; ~i; i = nxt[i]) ans.push_back(dfs(vv[i], r, 1));
  sort(ans.begin(), ans.end());
  if (ans[0] == -1) {
    puts("-1");
    return 0;
  }
  int cnt = unique(ans.begin(), ans.end()) - ans.begin();
  if (cnt > 2) puts("-1");
  int res = 0;
  for (int i = 0; i < cnt; ++i) res += ans[i];
  while (res % 2 == 0) res /= 2;
  cout << res << endl;
  return 0;
}
