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;
inline int read() {
  int x = 0, ch = getchar(), f = 1;
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
  return x * f;
}
const int N = 200005;
int n, dep[N], fa[N], stk[N], tp;
vector<int> E[N];
void dfs(int x, int f) {
  dep[x] = dep[f] + 1;
  fa[x] = f;
  for (int i = 0; i < E[x].size(); ++i)
    if (E[x][i] != f) dfs(E[x][i], x);
}
void calc(int x, int f) {
  dep[x] = 0;
  int lst = -1;
  for (int i = 0; i < E[x].size(); ++i) {
    int y = E[x][i];
    if (y == f) continue;
    calc(y, x);
    if (lst == -1) lst = dep[y];
    if (dep[y] != lst) {
      printf("-1\n");
      exit(0);
    }
  }
  dep[x] = lst + 1;
}
int main() {
  n = read();
  for (int i = 2; i <= n; ++i) {
    int u = read(), v = read();
    E[u].push_back(v);
    E[v].push_back(u);
  }
  dep[0] = -1;
  dfs(1, 0);
  int p = 1;
  for (int i = 1; i <= n; ++i)
    if (dep[i] > dep[p]) p = i;
  dfs(p, 0);
  int q = p;
  for (int i = 1; i <= n; ++i)
    if (dep[i] > dep[q]) q = i;
  int len = dep[q];
  for (int i = 1; i <= len / 2; ++i) q = fa[q];
  if (len & 1) {
    calc(q, fa[q]);
    calc(fa[q], q);
    printf("%d\n", len);
  } else {
    for (int i = 0; i < E[q].size(); ++i) {
      calc(E[q][i], q);
      stk[++tp] = dep[E[q][i]] + 1;
    }
    sort(stk + 1, stk + 1 + tp);
    tp = unique(stk + 1, stk + tp + 1) - stk - 1;
    if (tp > 2) {
      printf("-1\n");
      exit(0);
    }
    if (tp == 2) len = stk[1] + stk[2];
    while (len % 2 == 0) len >>= 1;
    printf("%d\n", len);
  }
  return 0;
}
