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;
map<int, set<pair<int, int> > > M;
vector<map<int, int> > w;
vector<vector<int> > T;
vector<int> deg;
int ans;
void remove(int x, int e) {
  if (x == e) {
    deg[x]--;
  } else {
    deg[x] = 0;
    --ans;
    for (int i = 0; i < T[x].size(); ++i) {
      if (deg[T[x][i]]) remove(T[x][i], e);
    }
  }
}
void update2(int x, int f, int l) {
  if (w[x].count(l) == 0) {
    M[x].insert({l, f});
  } else
    remove(f, x);
  if (deg[x] <= 2) M[x].clear();
}
void get(int x, int f, int l, int p, bool b) {
  if (deg[x] >= 3) {
    M[x].insert({l, f});
    ++w[x][l] = 1;
    if (b) update2(x, f, l);
  } else {
    for (int i = 0; i < T[x].size(); ++i) {
      if (T[x][i] != p and deg[T[x][i]]) {
        get(T[x][i], f, l + 1, x, b);
      }
    }
  }
}
void update(int x) {
  set<int> lel;
  set<pair<int, int> > s = M[x];
  int cur = -1;
  vector<pair<int, int> > vp;
  int l0, f0;
  for (set<pair<int, int> >::iterator it = s.begin(); it != s.end(); ++it) {
    pair<int, int> P = *it;
    int l = P.first, f = P.second;
    if (cur == -1) f0 = f, l0 = l;
    if (cur == l) {
      remove(f, x);
      vp.push_back({l, f});
    } else
      ++w[x][l];
    cur = l;
  }
  for (int i = 0; i < vp.size(); ++i) {
    M[x].erase(vp[i]);
  }
  if (deg[x] == 2) {
    get(f0, f0, 0, -1, true);
    M[x].clear();
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  ans = n;
  T = vector<vector<int> >(n);
  w.resize(n);
  deg = vector<int>(n, 0);
  for (int i = 0; i < n - 1; ++i) {
    int x, y;
    cin >> x >> y;
    --x, --y;
    ++deg[x];
    ++deg[y];
    T[x].push_back(y);
    T[y].push_back(x);
  }
  bool bbb = 1;
  for (int i = 0; i < n; ++i)
    if (deg[i] == 1) {
      get(i, i, 0, -1, false);
    }
  for (int i = 0; i < n; ++i)
    if (deg[i] >= 3) {
      update(i);
    }
  bool b = true;
  for (int i = 0; i < n; ++i)
    if (M[i].size() != 0) b = false;
  if (!b)
    cout << -1 << endl;
  else {
    while (ans % 2 == 0) {
      ans /= 2;
    }
    cout << (b ? ans - 1 : -1) << endl;
  }
}
