#include <bits/stdc++.h>
using namespace std;
vector<int> g[200005];
queue<pair<int, int> > q;
int deg[200005], a, n;
bool v[200005];
set<int> s[200005];
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
    deg[a]++, deg[b]++;
  }
  for (int i = 1; i <= n; i++)
    if (deg[i] == 1) q.push(pair<int, int>(i, 0));
  int c = 0, lst = -1;
  while (!q.empty()) {
    int x = q.front().first, d = q.front().second;
    q.pop();
    v[x] = true;
    lst = x, c++;
    for (auto y : g[x]) {
      if (v[y]) continue;
      deg[y]--;
      s[y].insert(d + 1);
      if (deg[y] == 1 and s[y].size() == 1) q.push(pair<int, int>(y, d + 1));
    }
  }
  if (c < n - 1)
    a = -1;
  else {
    if (c == n - 1)
      for (int i = 1; i <= n; i++)
        if (!v[i]) lst = i;
    if (s[lst].size() > 2)
      a = -1;
    else {
      for (auto e : s[lst]) a += e;
    }
  }
  while (a % 2 == 0) a /= 2;
  printf("%d\n", a);
}
