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;
int he[202333], nx[402333], to[402333], ec;
int root, n;
int fa[202333], dep[202333], md, mai;
void dfs(int x) {
  if (dep[x] > md) md = dep[x], mai = x;
  for (int e = he[x]; e; e = nx[e]) {
    if (to[e] != fa[x]) {
      fa[to[e]] = x;
      dep[to[e]] = dep[x] + 1;
      dfs(to[e]);
    }
  }
}
bool valid = true;
set<int> DP(int x) {
  int c = 0;
  set<int> R;
  for (int e = he[x]; e; e = nx[e]) {
    if (to[e] != fa[x]) {
      ++c;
      set<int> S = DP(to[e]);
      if (!valid) return R;
      for (auto it = S.begin(); valid && it != S.end(); ++it) {
        if (R.find(*it) == R.end()) R.insert(*it);
      }
    }
  }
  if (!c) R.insert(dep[x]);
  if (x != root && R.size() > 1) valid = false;
  return R;
}
int main() {
  cin >> n;
  for (int i = 1, u, v; i < n; ++i) {
    cin >> u >> v;
    nx[++ec] = he[u], he[u] = ec, to[ec] = v;
    nx[++ec] = he[v], he[v] = ec, to[ec] = u;
  }
  root = 1;
  dfs(root);
  md = dep[mai] = fa[mai] = 0;
  root = mai;
  dfs(root);
  while (dep[mai] != md / 2) mai = fa[mai];
  root = mai;
  md = dep[mai] = fa[mai] = 0;
  dfs(root);
  set<int> S = DP(root);
  if (S.size() > 2 || !valid)
    puts("-1");
  else {
    int ans = 0;
    for (auto it = S.begin(); it != S.end(); ++it) ans += *it;
    while (ans % 2 == 0) ans /= 2;
    printf("%d", ans);
  }
}
