#include <bits/stdc++.h>
using namespace std;
void write(int x) {
  if (x < 0) {
    putchar('-');
    x = -x;
  }
  if (x > 9) write(x / 10);
  putchar(x % 10 + '0');
}
int read() {
  int d = 0, w = 1;
  char c = getchar();
  for (; c < '0' || c > '9'; c = getchar())
    if (c == '-') w = -1;
  for (; c >= '0' && c <= '9'; c = getchar()) d = (d << 1) + (d << 3) + c - 48;
  return d * w;
}
void wln(int x) {
  write(x);
  putchar('\n');
}
void wrs(int x) {
  write(x);
  putchar(' ');
}
vector<int> a[200010], son[200010];
int f[200010], dep[200010], tmp, ma, flag, ans, g[200010], n;
void dfs(int k, int fa) {
  f[k] = fa;
  dep[k] = dep[fa] + 1;
  if (dep[k] > dep[ma]) ma = k;
  for (auto x : a[k])
    if (x != fa) dfs(x, k);
}
void dp(int k, int fa) {
  if (flag) return;
  for (auto x : a[k]) {
    if (x == fa) continue;
    dp(x, k);
    son[k].push_back(g[x]);
  }
  sort(son[k].begin(), son[k].end());
  int kk = unique(son[k].begin(), son[k].end()) - son[k].begin();
  if (k != tmp) {
    if (kk == 0) return;
    if (kk > 1) {
      flag = 1;
      return;
    }
    g[k] = son[k][0] + 1;
  } else {
    if (kk > 2) flag = 1;
    if (kk == 1) ans = son[k][0] + 1;
    if (kk == 2) ans = son[k][0] + son[k][1] + 2;
  }
}
signed main() {
  n = read();
  for (int i = 1; i < n; i++) {
    int x = read(), y = read();
    a[x].push_back(y);
    a[y].push_back(x);
  }
  dfs(1, 0);
  tmp = ma;
  ma = 0;
  dfs(tmp, 0);
  tmp = ma;
  for (; dep[tmp] != dep[ma] + 1 >> 1; tmp = f[tmp])
    ;
  dp(tmp, 0);
  if (!flag)
    for (; !(ans & 1); ans >>= 1)
      ;
  if (flag)
    write(-1);
  else
    write(ans);
  return 0;
}
