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>
#pragma comment(linker, "/STACK:268435456")
using namespace std;
template <typename T>
T sqr(const T &x) {
  return x * x;
}
template <typename T>
T my_abs(const T &x) {
  return x < 0 ? -x : x;
}
const int INF = (int)1e9;
const long long LINF = (long long)6e18;
const long long INF64 = LINF;
const long long INFLL = LINF;
const long double EPS = 1e-15;
const long double PI = 3.1415926535897932384626433832795;
const long double ME = 1e-5;
const long long MOD2 = (int)1e9 + 21;
const int SQN = 320;
const int LOGN = 17;
const int dx[] = {0, 1, 0, -1};
const int dy[] = {-1, 0, 1, 0};
const int N = (int)2e5 + 10;
const int M = 26;
const long long MOD = (int)1e9 + 7;
vector<int> g[N];
int n;
int d[N];
int len[N];
void dfs(int v, int p) {
  len[v] = -1;
  if (int(g[v].size()) == 1) {
    len[v] = 0;
    return;
  }
  for (int i = 0; i < int(int(g[v].size())); ++i) {
    int u = g[v][i];
    if (u == p) {
      continue;
    }
    dfs(u, v);
    if (len[v] == -1) {
      len[v] = len[u] + 1;
    } else if (len[v] != len[u] + 1) {
      printf("-1\n");
      exit(0);
    }
  }
}
void solve() {
  scanf("%d", &n);
  for (int i = 0; i < int(n - 1); ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--, v--;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  int st = 0;
  queue<int> q;
  memset(d, -1, sizeof(d));
  d[st] = 0;
  q.push(st);
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    for (int i = 0; i < int(int(g[v].size())); ++i) {
      int u = g[v][i];
      if (d[u] == -1) {
        d[u] = d[v] + 1;
        q.push(u);
      }
    }
  }
  st = 0;
  for (int v = 0; v < int(n); ++v) {
    if (d[v] > d[st]) {
      st = v;
    }
  }
  memset(d, -1, sizeof(d));
  d[st] = 0;
  q.push(st);
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    for (int i = 0; i < int(int(g[v].size())); ++i) {
      int u = g[v][i];
      if (d[u] == -1) {
        d[u] = d[v] + 1;
        q.push(u);
      }
    }
  }
  st = 0;
  for (int v = 0; v < int(n); ++v) {
    if (d[v] > d[st]) {
      st = v;
    }
  }
  int r = -1;
  for (int v = 0; v < int(n); ++v) {
    if (d[v] == d[st] / 2) {
      r = v;
      break;
    }
  }
  assert(r != -1);
  vector<int> lens;
  for (int i = 0; i < int(int(g[r].size())); ++i) {
    int u = g[r][i];
    dfs(u, r);
    lens.push_back(len[u] + 1);
  }
  sort(lens.begin(), lens.end());
  lens.erase(unique(lens.begin(), lens.end()), lens.end());
  if (int(lens.size()) > 2) {
    printf("-1\n");
    return;
  }
  int sum = 0;
  for (int i = 0; i < int(int(lens.size())); ++i) {
    sum += lens[i];
  }
  while (!(sum & 1)) {
    sum = sum >> 1;
  }
  printf("%d\n", sum);
}
int main() {
  ios_base::sync_with_stdio(false);
  srand((unsigned int)time(NULL));
  cout << setprecision(15) << fixed;
  solve();
  return 0;
}
