#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <cassert>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <unordered_set>
#include <unordered_map>

#define pb push_back
#define mp make_pair

#define f first
#define s second

#define pii pair<int, int>

using namespace std;

const int N = (int) 2e5 + 10;
const int MOD = (int) 1e9 + 7;

int n;
vector<int> g[N];

int dp[N];
int up[N];
int batya[N];

int combine(int a, int b) {
  if (a == 0 || b == 0)
    return a ? a : b;
  if (a == -1 || b == -1 || a != b)
    return -1;
  assert(a == b);
  return a;
}

void dfs(int v, int parent = 0) {
  batya[v] = parent;
  for (auto to : g[v]) {
    if (to == parent) continue;
    dfs(to, v);
    dp[v] = combine(dp[v], dp[to]);
  }
  if (dp[v] != -1) ++dp[v];
}

void calc_up(int v, int parent = 0) {
  vector<int> children;
  for (auto to : g[v]) {
    if (to == parent) continue;
    children.pb(to);
  }
  if (children.empty())
    return;
  vector<int> prefix;
  prefix.resize(children.size());
  for (int i = 0; i < prefix.size(); i++) {
    if (i) prefix[i] = prefix[i - 1];
    prefix[i] = combine(prefix[i], dp[children[i]]);
  }
  int suffix = 0;
  for (int i = (int) children.size() - 1; i >= 0; i--) {
    int to = children[i];
    int we = combine(suffix, i ? prefix[i - 1] : 0);
    up[to] = combine(we, up[v]);
    if (up[to] != -1) up[to]++;
    calc_up(to, v);
    suffix = combine(suffix, dp[children[i]]);
  }
}

int main() {
  #ifdef LOCAL
  freopen("in.txt", "r", stdin);
  //freopen("out", "w", stdout);
  #endif

  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    g[u].pb(v);
    g[v].pb(u);
  }
  dfs(1);
  calc_up(1);
  //for (int i = 1; i <= n; i++)
  //  cout << dp[i] << ' ';
  //cout << endl;
  //for (int i = 1; i <= n; i++)
  //  cout << up[i] << ' ';
  //cout << endl;
  //for (int i = 1; i <= n; i++)
  //  if (up[i] != -1) --up[i];
  int ans = MOD;
  for (int root = 1; root <= n; root++) {
    vector<int> deti;
    for (auto to : g[root]) {
      if (to == batya[root]) continue;
      deti.pb(dp[to]);
    }
    if (up[root])
      deti.pb(up[root]);
    sort(deti.begin(), deti.end());
    deti.resize(unique(deti.begin(), deti.end()) - deti.begin());
    if (deti.size() > 2) continue;
    if (deti.empty()) continue;
    if (deti[0] == -1) continue;
    int sum = 0;
    for (auto it : deti) sum += it;
    ans = min(ans, sum);
  }
  if (ans == MOD) {
    cout << -1;
    return 0;
  }
  while (ans % 2 == 0) ans /= 2;
  cout << ans;
  return 0;
}