#include <bits/stdc++.h>
using namespace std;
const long long inf = (long long)1e18;
const long long mod = (long long)1e9 + 7;
const double eps = (double)1e-9;
const double pi = acos(-1.0);
const int dx[] = {0, 0, 1, 0, -1};
const int dy[] = {0, 1, 0, -1, 0};
const int N = 300500;
int n, dp[N];
vector<int> g[N], l;
vector<pair<int, int> > gr, G, ga[N];
void dfs(int v, int pr = -1) {
  dp[v] = 1;
  for (int to : g[v]) {
    if (to != pr) {
      dfs(to, v);
      dp[v] += dp[to];
    }
  }
}
int dfs1(int v) {
  for (int to : g[v]) {
    if (dp[to] * 2 > n) {
      dp[v] -= dp[to];
      dp[to] += dp[v];
      return dfs1(to);
    }
  }
  return v;
}
void dfs2(int v, int pr, int gl = 0) {
  gr.push_back(make_pair(gl, v));
  for (int to : g[v]) {
    if (to != pr) {
      dfs2(to, v, gl + 1);
    }
  }
}
void checkv(int st) {
  gr.clear();
  dfs2(st, -1, 0);
  sort(gr.begin(), gr.end());
  for (int i = 0; i + 1 < n; ++i) {
    if (gr[i].first == gr[i + 1].first &&
        (int)g[gr[i].second].size() != (int)g[gr[i + 1].second].size())
      return;
  }
  cout << st << endl;
  exit(0);
}
int main() {
  cin.tie(NULL);
  cout.tie(NULL);
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i < n; ++i) {
    int x, y;
    cin >> x >> y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  dfs(1);
  int centroid = dfs1(1);
  checkv(centroid);
  for (int i = 1; i <= n; ++i)
    if ((int)g[i].size() == 1) l.push_back(i);
  for (int x : l) {
    int last = x;
    int cur = g[x][0];
    int dist = 1;
    while ((int)g[cur].size() == 2) {
      int nxt = g[cur][0];
      if (nxt == last) nxt = g[cur][1];
      dist++;
      last = cur;
      cur = nxt;
    }
    if (dist == n - 1) {
      checkv(x);
      cout << -1;
      return 0;
    }
    ga[cur].push_back(make_pair(x, dist));
    G.push_back(make_pair(dist, x));
  }
  for (int i = 1; i <= n; ++i) {
    if ((int)ga[i].size() == 1) {
      checkv(ga[i][0].first);
      cout << -1;
      return 0;
    }
  }
  for (int i = 0; i + 1 < (int)G.size(); ++i)
    if (G[i].first != G[i + 1].first) {
      checkv(G[i].second);
      checkv(G[i + 1].second);
      cout << -1;
      return 0;
    }
  cout << -1 << endl;
  return 0;
  return 0;
}
