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;
int read() {
  int x = 0, f = 1;
  char c = getchar();
  for (; !isdigit(c); c = getchar())
    if (c == '-') f = -1;
  for (; isdigit(c); c = getchar()) x = x * 10 + c - '0';
  return x * f;
}
const int MAXN = 200005;
queue<int> q;
set<int> s[MAXN];
int deg[MAXN];
bool vis[MAXN];
int nedge, head[MAXN];
struct Edge {
  int to, nxt;
} edge[MAXN * 2];
void add(int x, int y) {
  edge[++nedge].to = y;
  edge[nedge].nxt = head[x];
  head[x] = nedge;
}
int main() {
  int n = read();
  for (int i = 1; i < n; i++) {
    int x = read(), y = read();
    add(x, y);
    add(y, x);
    deg[x]++;
    deg[y]++;
  }
  for (int i = 1; i <= n; i++)
    if (deg[i] == 1) {
      q.push(i);
      s[i].insert(0);
    }
  while (!q.empty()) {
    int now = q.front();
    q.pop();
    vis[now] = 1;
    for (int i = head[now]; i; i = edge[i].nxt) {
      int u = edge[i].to;
      if (vis[u]) continue;
      s[u].insert(*s[now].begin() + 1);
      deg[u]--;
      if (deg[u] == 1 && s[u].size() == 1) q.push(u);
    }
  }
  int ans = 0;
  bool f = 0;
  for (int i = 1; i <= n; i++) {
    if (!s[i].size()) return puts("-1");
    if (s[i].size() > 2) return puts("-1");
    if (s[i].size() == 1) ans = max(ans, *s[i].begin());
    if (s[i].size() == 2) {
      if (f) return puts("-1"), 0;
      f = 1;
      ans = max(ans, *s[i].begin() + *s[i].rbegin());
    }
  }
  while (ans % 2 == 0) ans /= 2;
  printf("%d", ans);
}
