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;
template <class C>
void mini(C &a4, C b4) {
  a4 = min(a4, b4);
}
template <class C>
void maxi(C &a4, C b4) {
  a4 = max(a4, b4);
}
template <class TH>
void _dbg(const char *sdbg, TH h) {
  cerr << sdbg << "=" << h << "\n";
}
template <class TH, class... TA>
void _dbg(const char *sdbg, TH h, TA... a) {
  while (*sdbg != ',') cerr << *sdbg++;
  cerr << "=" << h << ",";
  _dbg(sdbg + 1, a...);
}
template <class T>
ostream &operator<<(ostream &os, vector<T> V) {
  os << "[";
  for (auto vv : V) os << vv << ",";
  return os << "]";
}
template <class L, class R>
ostream &operator<<(ostream &os, pair<L, R> P) {
  return os << "(" << P.first << "," << P.second << ")";
}
const long long MaxN = 2e5 + 6;
long long N;
vector<long long> adj[MaxN];
long long deg[MaxN];
long long pathLen[MaxN];
bool lit[MaxN];
bool stopVert[MaxN];
bool vis[MaxN];
set<long long> pathLens[MaxN];
vector<long long> pathAdj[MaxN];
long long dfs(long long v) {
  (v);
  long long result = 1;
  vis[v] = true;
  for (long long s : pathAdj[v]) {
    if (vis[s]) {
      continue;
    }
    result += dfs(s);
  }
  return result;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(11);
  if (0) cout << fixed << setprecision(6);
  cin >> N;
  for (long long i = 1; i < N; i++) {
    long long u, v;
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
    deg[u]++;
    deg[v]++;
  }
  queue<long long> leaves;
  for (long long i = 1; i <= N; i++) {
    lit[i] = true;
    if (deg[i] == 1) {
      leaves.push(i);
      pathLen[i] = 1;
      pathLens[i].insert(1);
    }
  }
  long long numProc = 0;
  while (!leaves.empty()) {
    if (numProc == N - 1) {
      break;
    }
    numProc++;
    long long v = leaves.front();
    leaves.pop();
    lit[v] = false;
    for (long long s : adj[v]) {
      if (lit[s]) {
        long long l = pathLen[v] + 1;
        if (!pathLens[s].count(l)) {
          pathLens[s].insert(l);
          (s, v);
          pathAdj[v].push_back(s);
          pathAdj[s].push_back(v);
        }
        deg[s]--;
        if (deg[s] == 1 && ((long long)(pathLens[s]).size()) == 1) {
          pathLen[s] = *pathLens[s].begin();
          leaves.push(s);
        }
      }
    }
  }
  long long cntStop = 0;
  for (long long i = 1; i <= N; i++) {
    if (((long long)(pathLens[i]).size()) > 1) {
      cntStop++;
    }
    if (((long long)(pathAdj[i]).size()) > 2 || cntStop >= 2) {
      cout << "-1\n";
      return 0;
    }
  }
  for (long long i = 1; i <= N; i++) {
    if (lit[i]) {
      long long ans = dfs(i) - 1;
      assert(ans);
      while (ans % 2 == 0) {
        ans /= 2;
      }
      cout << ans << "\n";
      return 0;
    }
  }
  assert(false);
}
