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 = 200002;
struct node {
  int to, ne;
} e[N << 1];
int n, i, x, y, s, rt, h[N], tot;
inline char gc() {
  static char buf[100000], *p1 = buf, *p2 = buf;
  return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 100000, stdin), p1 == p2)
             ? EOF
             : *p1++;
}
inline int rd() {
  int x = 0, fl = 1;
  char ch = gc();
  for (; ch < 48 || ch > 57; ch = gc())
    if (ch == '-') fl = -1;
  for (; 48 <= ch && ch <= 57; ch = gc()) x = (x << 3) + (x << 1) + (ch ^ 48);
  return x * fl;
}
inline void wri(int a) {
  if (a < 0) a = -a, putchar('-');
  if (a >= 10) wri(a / 10);
  putchar(a % 10 | 48);
}
inline void wln(int a) {
  wri(a);
  puts("");
}
int dfs(int u, int fa) {
  set<int> S;
  for (int i = h[u], v; i; i = e[i].ne)
    if ((v = e[i].to) != fa) {
      int t = dfs(v, u);
      if (t == -1) return -1;
      S.insert(t + 1);
    }
  if (S.size() > 2) return -1;
  if (!S.size()) return 0;
  if (S.size() == 1) return *S.begin();
  if (S.size() == 2 && !fa) return *S.rbegin() + *S.begin();
  rt = u;
  return -1;
}
void add(int x, int y) {
  e[++tot] = (node){y, h[x]};
  h[x] = tot;
}
int main() {
  n = rd();
  for (i = 1; i < n; i++) x = rd(), y = rd(), add(x, y), add(y, x);
  s = dfs(1, 0);
  if (s == -1 && rt) s = dfs(rt, 0);
  printf("%d", s / (s & -s));
}
