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 MAX = 200200;
vector<int> adj[MAX];
int ch[MAX], sz, from[MAX], dpthMx[MAX], dpthMn[MAX], n;
void dfs(int cur, int par) {
  for (auto i : adj[cur])
    if (i != par) {
      dfs(i, cur);
      dpthMn[cur] = min(dpthMn[cur], dpthMn[i] + 1);
      dpthMx[cur] = max(dpthMx[cur], dpthMx[i] + 1);
    }
  if (dpthMn[cur] == MAX) dpthMn[cur] = 0;
}
pair<int, int> dfs0(int cur, int par, int d) {
  from[cur] = par;
  pair<int, int> ret(d, cur);
  for (auto i : adj[cur])
    if (i != par) ret = max(ret, dfs0(i, cur, d + 1));
  return ret;
}
int main() {
  scanf("%d", &n);
  fill(dpthMn, dpthMn + n + 1, MAX);
  for (int i = 1, u, v; i < n; ++i) {
    scanf("%d%d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  pair<int, int> diam = dfs0(dfs0(1, 0, 0).second, 0, 0);
  while (diam.first > 0) diam.first -= 2, diam.second = from[diam.second];
  dfs(diam.second, 0);
  for (auto i : adj[diam.second]) {
    if (dpthMx[i] != dpthMn[i]) return puts("-1"), 0;
    ch[sz++] = dpthMx[i] + 1;
  }
  sort(ch, ch + sz);
  sz = unique(ch, ch + sz) - ch;
  if (sz > 2) return puts("-1"), 0;
  ch[sz] = 0;
  int ans = ch[0] + ch[1];
  while (!(ans & 1)) ans >>= 1;
  printf("%d\n", ans);
  return 0;
}
