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 = 200005;
vector<int> adj[N];
unordered_map<int, vector<int>> tails[N];
int head[N], head2[N], dist[N], tailCnt[N];
pair<pair<int, int>, int> findJunction(int u, int p) {
  int origU = u, origP = p;
  int len = 1;
  p = origU;
  u = adj[origU][0];
  while (adj[u].size() == 2) {
    int np = u;
    int nu = (adj[u][0] == p ? adj[u][1] : adj[u][0]);
    p = np;
    u = nu;
    len++;
  }
  return pair<pair<int, int>, int>(pair<int, int>(p, u), len);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    u--;
    v--;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  int nRemain = n - 1;
  int nJunction = 0;
  for (int i = 0; i < n; i++) {
    if (adj[i].size() > 2) {
      nJunction++;
    }
    tailCnt[i] = adj[i].size();
  }
  if (nJunction > 0) {
    queue<pair<int, int>> nxtTails;
    for (int u = 0; u < n; u++) {
      if (adj[u].size() == 1) {
        pair<pair<int, int>, int> res = findJunction(u, -1);
        int pp = res.first.first;
        int p = res.first.second;
        int d = res.second;
        head2[u] = pp;
        head[u] = p;
        dist[u] = d;
        if (tails[p].count(d) > 0) {
          nxtTails.push(pair<int, int>(d, p));
        }
        tails[p][d].push_back(u);
      }
    }
    while (!nxtTails.empty()) {
      pair<int, int> curItem = nxtTails.front();
      nxtTails.pop();
      int d = curItem.first;
      int p = curItem.second;
      int u1 = tails[p][d][0];
      int u2 = tails[p][d].back();
      if (u1 == u2) continue;
      int prv = u2;
      int cur = adj[u2][0];
      while (prv != p) {
        adj[prv].clear();
        nRemain--;
        int nprv = cur;
        int ncur = (adj[cur][0] == prv ? adj[cur][1] : adj[cur][0]);
        prv = nprv;
        cur = ncur;
      }
      tails[p][d].pop_back();
      tailCnt[p]--;
      if (tailCnt[p] == 2) {
        tails[p].clear();
        tailCnt[p] = 0;
        nJunction--;
        if (nJunction == 0) {
          break;
        }
        pair<pair<int, int>, int> res = findJunction(p, head2[u1]);
        int npp = res.first.first;
        int np = res.first.second;
        int nd = res.second + d;
        head2[u1] = npp;
        head[u1] = np;
        dist[u1] = nd;
        if (tails[np].count(nd) > 0 && tails[np][nd].size() > 0) {
          nxtTails.push(pair<int, int>(nd, np));
        }
        tails[np][nd].push_back(u1);
      }
    }
  }
  if (nJunction != 0) {
    cout << -1 << endl;
    return 0;
  }
  while (nRemain % 2 == 0) {
    nRemain /= 2;
  }
  cout << nRemain << endl;
}
