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;
vector<int> g[200005];
int d[200005];
bool check[200005];
queue<int> q;
int first_err = -1;
set<int> s[200005];
int dfs(int u, int par) {
  for (int i = 0; i < (int)g[u].size(); i++) {
    int v = g[u][i];
    if (v == par) continue;
    s[u].insert(dfs(v, u));
  }
  if (s[u].empty())
    return 1;
  else {
    if (par == -1) {
      if (s[u].size() > 2)
        return -1;
      else {
        int res = 0;
        for (set<int>::iterator it = s[u].begin(); it != s[u].end(); ++it) {
          if ((*it) == -1) return -1;
          res += (*it);
        }
        return res;
      }
    } else {
      if (s[u].size() > 1) {
        if (first_err == -1) first_err = u;
        return -1;
      } else {
        set<int>::iterator it = s[u].begin();
        if ((*it) == -1) return -1;
        return (*it) + 1;
      }
    }
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    d[x]++;
    d[y]++;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  for (int i = 1; i <= n; i++)
    if (d[i] == 1) q.push(i);
  int last = -1;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    check[u] = true;
    last = u;
    for (int i = 0; i < g[u].size(); i++) {
      int v = g[u][i];
      if (check[v]) continue;
      d[v]--;
      if (d[v] == 1) q.push(v);
    }
  }
  int r1 = dfs(last, -1);
  if (r1 != -1)
    while (r1 % 2 == 0) r1 /= 2;
  int r2 = -1;
  if (first_err != -1) {
    for (int i = 1; i <= n; i++) s[i].clear();
    r2 = dfs(first_err, -1);
    if (r2 != -1)
      while (r2 % 2 == 0) r2 /= 2;
  }
  printf("%d\n", max(r1, r2));
  return 0;
}
