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 MAX = 2e5 + 5;
set<int> edge[MAX];
set<int> dis[MAX];
queue<int> que;
bool vi[MAX];
int re(int x) {
  while (x % 2 == 0) x /= 2;
  return x;
}
int solve() {
  memset(vi, false, sizeof(vi));
  while (!que.empty()) {
    int u = que.front();
    que.pop();
    if (vi[u]) continue;
    if (edge[u].size() == 1) {
      if (dis[u].size() == 1) {
        int v = *edge[u].begin();
        edge[u].erase(v);
        edge[v].erase(u);
        dis[v].insert(*dis[u].begin() + 1);
        que.push(v);
        vi[u] = true;
      }
    } else if (edge[u].empty()) {
      if (dis[u].size() >= 3) {
        return -1;
      }
      if (dis[u].size() == 1) return re(*dis[u].begin());
      return re(*dis[u].begin() + *dis[u].rbegin());
    }
  }
  return -1;
}
int n;
int main() {
  scanf("%d", &n);
  int i;
  int u, v;
  for (i = 1; i <= n - 1; i++) {
    scanf("%d %d", &u, &v);
    edge[u].insert(v);
    edge[v].insert(u);
  }
  for (i = 1; i <= n; i++) {
    if (edge[i].size() == 1) {
      que.push(i);
      dis[i].insert(0);
    }
  }
  printf("%d\n", solve());
}
