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 MaxN = 200005;
struct Edge {
  int to, nxt;
} e[MaxN << 1];
int n, head[MaxN], cnt, d[MaxN], dl[MaxN], dr[MaxN], ans, l, r, rt;
inline void Add(int x, int y) {
  e[++cnt].to = y;
  e[cnt].nxt = head[x];
  head[x] = cnt;
}
inline void AddEdge(int x, int y) {
  Add(x, y);
  Add(y, x);
}
void dfs(int x, int fa, int dep, int *d) {
  d[x] = dep;
  for (int i = head[x]; i; i = e[i].nxt)
    if (e[i].to != fa) dfs(e[i].to, x, dep + 1, d);
}
inline int Solve(int x, int fa) {
  vector<int> v;
  for (int i = head[x]; i; i = e[i].nxt)
    if (e[i].to != fa) v.push_back(Solve(e[i].to, x));
  sort(v.begin(), v.end());
  v.resize(unique(v.begin(), v.end()) - v.begin());
  if (x != fa) {
    if (v.size() > 1) puts("-1"), exit(0);
    if (v.empty()) return 1;
    return v.front() + 1;
  }
  if (v.size() > 2) return -1;
  return v.front() + v.back();
}
void Init() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    AddEdge(u, v);
  }
}
void Main() {
  dfs(1, 0, 0, d);
  for (int i = 1; i <= n; ++i)
    if (d[i] > d[l]) l = i;
  dfs(l, 0, 0, dl);
  for (int i = 1; i <= n; ++i)
    if (dl[i] > dl[r]) r = i;
  dfs(r, 0, 0, dr);
  rt = l;
  for (int i = 1; i <= n; ++i)
    if (dl[i] + dr[i] == dl[r] && min(dl[i], dr[i]) > min(dl[rt], dr[rt]))
      rt = i;
  ans = Solve(rt, rt);
  while (ans && !(ans & 1)) ans >>= 1;
  cout << ans << endl;
}
int main() {
  Init();
  Main();
  return 0;
}
