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;
vector<int> adj[200010];
int vis[200010];
int depth[200010];
int depth2[200010];
int max_deep, max_depth, centre;
void dfs(int in, int d) {
  vis[in] = 1;
  if (d > max_depth) {
    max_depth = d;
    max_deep = in;
  }
  depth[in] = d;
  for (int j = 0; j < adj[in].size(); j++) {
    if (vis[adj[in][j]]) continue;
    dfs(adj[in][j], 1 + d);
  }
}
void dfs2(int in, int d) {
  vis[in] = 1;
  depth2[in] = d;
  for (int j = 0; j < adj[in].size(); j++) {
    if (vis[adj[in][j]]) continue;
    dfs2(adj[in][j], 1 + d);
  }
}
int dfs_final(int in, int depth) {
  vis[in] = 1;
  vector<int> depths;
  for (int i = 0; i < adj[in].size(); i++) {
    if (vis[adj[in][i]]) continue;
    depths.push_back(dfs_final(adj[in][i], depth + 1));
  }
  sort(depths.begin(), depths.end());
  if (in != centre) {
    if (depths.size() == 0) {
      return depth;
    }
    if (depths[0] != depths.back()) {
      printf("-1\n");
      exit(0);
    }
    return depths[0];
  }
  int cnt = 0;
  for (int i = 0; i + 1 < depths.size(); i++)
    if (depths[i] != depths[i + 1]) cnt++;
  cnt++;
  if (cnt == 1)
    return depths[0];
  else if (cnt == 2)
    return depths[0] + depths.back();
  else {
    printf("-1\n");
    exit(0);
  }
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs(1, 0);
  int s1 = max_deep;
  max_depth = 0;
  memset(vis, 0, sizeof vis);
  dfs(s1, 0);
  int s2 = max_deep;
  memset(vis, 0, sizeof vis);
  dfs2(s2, 0);
  for (int i = 1; i <= n; i++) {
    if (depth[i] + depth2[i] == depth[s2] && depth[i] == max_depth / 2) {
      centre = i;
      break;
    }
  }
  memset(vis, 0, sizeof vis);
  int ans = dfs_final(centre, 0);
  while (ans % 2 == 0 && ans) {
    ans /= 2;
  }
  printf("%d\n", ans);
  return 0;
}
