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, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
inline void wrote(int x) {
  if (x < 0) putchar('-'), x = -x;
  if (x >= 10) wrote(x / 10);
  putchar(x % 10 + '0');
}
inline void writeln(int x) {
  wrote(x);
  puts("");
}
const int N = 400010;
set<int> s[N];
int vis[N], dfn[N], head[N], nxt[N], vet[N], q[N], he, ta, n, tot, ans;
void insert(int x, int y) {
  nxt[++tot] = head[x];
  head[x] = tot;
  vet[tot] = y;
  ++dfn[x];
}
int main() {
  n = read();
  for (int i = 2; i <= n; ++i) {
    int x = read(), y = read();
    insert(x, y);
    insert(y, x);
  }
  for (int i = 1; i <= n; ++i)
    if (1 == dfn[i]) q[++ta] = i, s[i].insert(0);
  while (he != ta) {
    int x = q[++he];
    vis[x] = 1;
    for (int i = head[x]; i; i = nxt[i])
      if (!vis[vet[i]]) {
        --dfn[vet[i]];
        s[vet[i]].insert(*s[x].begin() + 1);
        if (dfn[vet[i]] == 1 && s[vet[i]].size() == 1) q[++ta] = vet[i];
      }
  }
  int sz = 0;
  for (int i = 1; i <= n; ++i) {
    if (s[i].size() == 0 || s[i].size() > 2) return puts("-1"), 0;
    if (s[i].size() == 1) ans = max(ans, *s[i].begin());
    if (s[i].size() == 2) ans = max(ans, *s[i].begin() + *s[i].rbegin()), ++sz;
  }
  if (sz > 1) return puts("-1"), 0;
  while (!(ans & 1)) ans >>= 1;
  writeln(ans);
}
