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;
vector<int> v[200010];
vector<pair<int, int> > q;
int n;
int dist[200010];
inline void del() {
  vector<pair<int, int> > qqq;
  qqq.swap(q);
}
inline void dfs(int nod, int tata) {
  dist[nod] = 1;
  for (auto &it : v[nod]) {
    if (it == tata) continue;
    dfs(it, nod);
    if (dist[nod] >= 2000000000) continue;
    int x = dist[it];
    if (x >= 2000000000) {
      dist[nod] = 2000000000;
      continue;
    }
    ++x;
    if (dist[nod] != 1) {
      if (dist[nod] != x) dist[nod] = 2000000000;
    } else
      dist[nod] = x;
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int x, y;
    scanf("%d %d", &x, &y);
    v[x].push_back(y);
    v[y].push_back(x);
  }
  dfs(1, -1);
  int nod = 1, tata = 0, mi = 2000000000;
  for (;;) {
    int nr = 0;
    for (auto &it : v[nod]) {
      q.push_back(make_pair(dist[it], it));
      if (dist[it] >= 2000000000) ++nr;
    }
    if (nr > 1) break;
    sort(q.begin(), q.end());
    int x = 0, z = -1;
    for (int i = 0; i < q.size() - 1; ++i) {
      int it = q[i].first;
      if (!x) x = it;
      if (x != it) {
        if (z == -1 || z == it)
          z = it;
        else
          x = z = 2000000000;
      }
    }
    int y = x, w = z, it = q.back().first;
    if (!x) x = it;
    if (x != it) {
      if (z == -1 || z == it)
        z = it;
      else
        x = z = 2000000000;
    }
    if (z >= 2000000000) x = z;
    if (x >= 2000000000)
      ;
    else {
      if (z == -1) {
        for (; x % 2 == 0 && x > 0; x /= 2)
          ;
        mi = min(mi, x);
      } else
        mi = min(mi, x + z);
    }
    if (w > -1) break;
    if (q.back().second == tata) break;
    tata = nod;
    nod = q[q.size() - 1].second;
    ++y;
    dist[tata] = y;
    del();
  }
  if (mi >= 2000000000)
    printf("-1\n");
  else
    printf("%d\n", mi);
  return 0;
}
