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;
int n, deep, pos, pre[222222], root, gg;
vector<int> g[222222];
set<int> s[222222];
set<int>::iterator it;
void init(int u, int fa, int cnt) {
  if (cnt > deep) deep = cnt, pos = u;
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == fa) continue;
    pre[v] = u;
    init(v, u, cnt + 1);
  }
}
int dfs(int u, int fa) {
  if (gg) return -1;
  if (u != root && g[u].size() == 1) return 0;
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == fa) continue;
    s[u].insert(dfs(v, u) + 1);
    if (u != root && s[u].size() > 1) {
      gg = 1;
      return -1;
    }
  }
  return *s[u].begin();
}
int main() {
  while (~scanf("%d", &n)) {
    for (int i = 1; i <= n; i++) g[i].clear(), s[i].clear();
    for (int i = 1; i < n; i++) {
      int u, v;
      scanf("%d%d", &u, &v);
      g[u].push_back(v), g[v].push_back(u);
    }
    deep = 0;
    init(1, 1, 0);
    deep = 0;
    init(pos, pos, 0);
    root = pos;
    for (int i = 1; i <= deep / 2; i++) root = pre[root];
    gg = 0;
    dfs(root, root);
    if (s[root].size() > 2) gg = 1;
    if (gg)
      printf("-1\n");
    else {
      deep = 0;
      for (it = s[root].begin(); it != s[root].end(); it++) deep += *it;
      while (deep % 2 == 0) deep /= 2;
      printf("%d\n", deep);
    }
  }
  return 0;
}
