#include <bits/stdc++.h>
using namespace std;
const int INF = 1E9 + 10;
const int N = 2E5 + 10;
int leave[N];
map<int, int> state[N];
int n, f[N], g[N];
vector<int> G[N];
void dfs1(int u, int fa) {
  if (G[u].size() == 1 && G[u][0] == fa) {
    leave[u] = 1;
  }
  state[u].clear();
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    dfs1(v, u);
    state[u][f[v]]++;
  }
  if (state[u].size() >= 2 || state[u].begin()->first == -1) {
    f[u] = -1;
  } else {
    if (state[u].size() == 1)
      f[u] = state[u].begin()->first + 1;
    else
      f[u] = 0;
  }
}
void dfs2(int u, int fa) {
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    map<int, int> make_pair = state[u];
    if (make_pair.size() > 2 || g[u] == -1) {
      g[v] = -1;
      continue;
    }
    make_pair[f[v]]--;
    int cnt = 0, val = 0;
    for (map<int, int>::iterator it = make_pair.begin(); it != make_pair.end();
         it++) {
      if (it->second == 0) {
        continue;
      } else {
        cnt++;
        val = it->first;
      }
    }
    if (cnt == 1 && val != -1) {
      if (g[u] == 0 || g[u] == val + 1) {
        g[v] = val + 2;
      } else {
        g[v] = -1;
      }
    } else if (cnt == 0) {
      g[v] = g[u] + 1;
    } else {
      g[v] = -1;
    }
  }
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    dfs2(v, u);
  }
}
int gen(int u) {
  if (u == 0) return 0;
  if (u & 1)
    return u;
  else
    return gen(u / 2);
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  dfs1(1, -1);
  dfs2(1, -1);
  int ans = n + 10;
  for (int i = 1; i <= n; i++) {
    if (i == 1) {
      if (f[i] != -1) ans = min(ans, gen(f[i]));
      continue;
    }
    if (g[i] != -1) {
      state[i][g[i] - 1]++;
      vector<int> nu;
      bool flag = true;
      if (state[i].size() > 3) continue;
      for (map<int, int>::iterator it = state[i].begin(); it != state[i].end();
           it++) {
        if (it->first == -1 && it->second > 0) flag = false;
        if (it->second == 0 || it->first == -1) {
          continue;
        } else {
          if (nu.size() <= 3) {
            nu.push_back(it->first);
          }
        }
      }
      if (flag == false) continue;
      if (nu.size() == 3)
        continue;
      else if (nu.size() == 2)
        ans = min(ans, gen(nu[0] + nu[1] + 2));
      else if (nu.size() == 1) {
        if (!leave[i])
          ans = min(ans, gen(2 * nu[0] + 2));
        else
          ans = min(ans, gen(nu[0] + 1));
      }
    }
  }
  if (ans == n + 10)
    puts("-1");
  else
    printf("%d\n", ans);
  return 0;
}
