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 = 323456;
const int inf = (int)1e9 + 7;
int n;
int d[N], prv = -1, bad;
queue<int> q;
vector<int> g[N];
vector<int> all;
int bfs(int s) {
  for (int i = 1; i <= n; ++i) {
    d[i] = inf;
  }
  d[s] = 0;
  q.push(s);
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    for (int i : g[v]) {
      if (d[i] == inf) {
        d[i] = d[v] + 1;
        q.push(i);
      }
    }
  }
  int mx = 0;
  for (int i = 1; i <= n; ++i) {
    if (!mx || d[mx] < d[i]) {
      mx = i;
    }
  }
  return mx;
}
int diam() {
  int f = bfs(1);
  int s = bfs(f);
  for (int i = 1; i <= n; ++i) {
    if ((d[s] / 2) == d[i]) {
      return i;
    }
  }
  return -1;
}
int get(int x) {
  while (x % 2) {
    x = x / 2 + 1;
  }
  return x;
}
void go(int v, int p, int h) {
  int leaf = 1;
  for (int i : g[v]) {
    if (i == p) {
      continue;
    }
    leaf = 0;
    go(i, v, h + 1);
  }
  if (leaf) {
    if (prv != -1 && h != prv) {
      bad = 1;
    }
    prv = h;
    all.push_back(h);
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int x, y;
    scanf("%d %d", &x, &y);
    g[x].push_back(y);
    g[y].push_back(x);
  }
  int d = diam();
  assert(d > 0);
  for (int i : g[d]) {
    prv = -1;
    go(i, d, 1);
  }
  sort(all.begin(), all.end());
  all.resize(unique(all.begin(), all.end()) - all.begin());
  if ((int)all.size() > 2 || bad) {
    printf("-1");
  } else if ((int)all.size() == 2) {
    printf("%d", get(all[0] + all[1] + 1) - 1);
  } else {
    printf("%d", get(all[0] + 1) - 1);
  }
  return 0;
}
