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;
using namespace std;
const int MN = 2e5 + 44;
vector<int> graf[MN];
void err() {
  printf("-1\n");
  exit(0);
}
int equal(int x, int y) {
  int val = -1;
  for (auto v : graf[x]) {
    if (v != y) {
      int curr = equal(v, x);
      if (curr != val && val != -1) {
        ;
        err();
      }
      val = curr;
    }
  }
  return val + 1;
}
pair<int, int> furthest(int x, int y = -1) {
  pair<int, int> res = make_pair(-1, x);
  for (auto v : graf[x])
    if (v != y) res = max(res, furthest(v, x));
  res.first++;
  return res;
}
bool dfs_path(int x, int y, int dest, vector<int>& path) {
  if (x == dest) {
    path.push_back(x);
    return true;
  }
  for (auto v : graf[x]) {
    if (v != y) {
      if (dfs_path(v, x, dest, path)) {
        path.push_back(x);
        return true;
      }
    }
  }
  return false;
}
vector<int> find_path(int a, int b) {
  vector<int> path;
  dfs_path(a, -1, b, path);
  return path;
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < (n - 1); i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    graf[a].push_back(b);
    graf[b].push_back(a);
  }
  int a = furthest(1, -1).second;
  int b = furthest(a, -1).second;
  vector<int> diameter = find_path(a, b);
  int res = 0;
  if (diameter.size() % 2) {
    int center = diameter[diameter.size() / 2];
    ;
    set<int> a;
    for (auto x : graf[center]) {
      a.insert(equal(x, center));
      if (a.size() > 2) {
        ;
        err();
      }
    }
    for (auto second : a) {
      ;
      res += 1 + second;
    }
  } else {
    int center1 = diameter[diameter.size() / 2 - 1],
        center2 = diameter[diameter.size() / 2];
    ;
    res = 1 + equal(center1, center2) + equal(center2, center1);
  };
  while (res % 2 == 0) res /= 2;
  printf("%d\n", res);
}
