#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);
}
