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 N = 201000;
const int M = 610000;
const int inf = 0x3f3f3f3f;
const int mod = 1000000007;
void MOD(long long &a) {
  if (a >= mod) a -= mod;
}
void ADD(long long &a, long long b) {
  a += b;
  MOD(a);
}
long long qpow(long long a, long long b) {
  long long ans = 1;
  while (b) {
    if (b & 1) ans = ans * a % mod;
    a = a * a % mod;
    b /= 2;
  }
  return ans;
}
long long qpow(long long a, long long b, long long c) {
  long long ans = 1;
  while (b) {
    if (b & 1) ans = ans * a % c;
    a = a * a % c;
    b /= 2;
  }
  return ans;
}
int n, head[N], tot;
struct EDGE {
  int to, nex;
} e[N * 2];
vector<int> diam;
int dist[N], pre[N];
void add(int u, int v) {
  e[tot].to = v;
  e[tot].nex = head[u];
  head[u] = tot++;
}
void dfs1(int x, int f, int &v) {
  dist[x] = dist[f] + 1;
  if (dist[x] > dist[v]) v = x;
  for (int i = head[x]; i != -1; i = e[i].nex) {
    int y = e[i].to;
    if (y == f) continue;
    pre[y] = x;
    dfs1(y, x, v);
  }
}
int dfs(int x, int f) {
  set<int> s;
  for (int i = head[x]; i != -1; i = e[i].nex) {
    int y = e[i].to;
    if (y == f) continue;
    int z = dfs(y, x);
    if (z == -1) return -1;
    s.insert(z + 1);
  }
  if (((int)s.size()) == 0)
    return 0;
  else if (((int)s.size()) == 1)
    return *(s.begin());
  else {
    if (x == diam[((int)diam.size()) / 2] && ((int)s.size()) == 2) {
      auto it = s.begin();
      int ans = 0;
      ans += *(it);
      it++;
      ans += *(it);
      return ans;
    } else
      return -1;
  }
}
int main() {
  memset(head, -1, sizeof(head));
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    add(u, v);
    add(v, u);
  }
  int x = 1, y;
  dfs1(1, 1, x);
  y = x;
  dfs1(x, x, y);
  diam.push_back(y);
  while (y != x) {
    diam.push_back(pre[y]);
    y = pre[y];
  }
  x = dfs(diam[((int)diam.size()) / 2], 0);
  if (x == -1)
    printf("-1\n");
  else {
    while (x % 2 == 0) x /= 2;
    printf("%d\n", x);
  }
}
