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;
long long pwr(long long base, long long p, long long mod = (1000000007LL)) {
  long long ans = 1;
  while (p) {
    if (p & 1) ans = (ans * base) % mod;
    base = (base * base) % mod;
    p /= 2;
  }
  return ans;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
int n, root, deg[200005], pathlen[200005];
set<int> adj[200005];
map<int, int> paths[200005];
void dfs(int v) {
  if (adj[v].empty()) {
    pathlen[v] = 0;
    return;
  }
  for (auto vv : adj[v]) adj[vv].erase(v);
  for (auto vv : adj[v]) {
    dfs(vv);
    if ((int)paths[vv].size() > 1) {
      printf("-1\n");
      exit(0);
    }
    paths[v][pathlen[vv]] = vv;
  }
  for (auto it : paths[v]) pathlen[v] = 1 + it.first;
}
int main() {
  scanf("%d", &n);
  if (n == 1) {
    printf("0\n");
    return 0;
  }
  if (n == 2 || n == 3) {
    printf("1\n");
    return 0;
  }
  int e = n - 1;
  while (e--) {
    int a, b;
    scanf("%d%d", &a, &b);
    deg[a]++;
    deg[b]++;
    adj[a].insert(b);
    adj[b].insert(a);
    if (deg[a] > 2) root = a;
  }
  if (root == 0) {
    int len = n - 1;
    while (len > 0 && len % 2 == 0) len /= 2;
    printf("%d\n", len);
    return 0;
  }
  dfs(root);
  if (paths[root].size() > 2) {
    printf("-1\n");
    return 0;
  }
  int len = 0;
  for (auto x : paths[root]) len += x.first + 1;
  while (len > 0 && len % 2 == 0) len /= 2;
  printf("%d\n", len);
  return 0;
}
