10
4 2
7 4
2 6
2 5
4 8
10 3
2 9
9 1
5 10
 10
5 10
7 8
8 3
2 6
3 2
9 7
4 5
10 1
6 4
 4
4 1
4 3
4 2
 3
3 1
1 2
 9
1 2
1 3
1 4
1 5
1 6
6 7
6 8
8 9
 5
1 5
2 3
2 4
1 2
 8
6 1
4 7
4 8
8 5
7 6
4 3
4 2
 7
5 6
5 7
5 1
7 4
6 3
3 2
 3
1 3
3 2
 2
1 2
 5
5 4
4 3
3 1
5 2
 6
1 6
3 1
6 4
5 3
2 5
 11
8 9
2 7
1 11
3 2
9 1
8 5
8 6
5 4
4 10
8 3
 11
11 9
6 7
7 1
8 11
5 6
3 5
9 3
10 8
2 4
4 10
 12
12 6
6 7
8 11
4 8
10 4
12 3
2 10
6 2
12 9
4 1
9 5

-1
 9
 1
 1
 3
 3
 -1
 -1
 1
 1
 1
 5
 1
 5
 -1

#include <bits/stdc++.h>
using namespace std;
int n, tam[606060], ev[606060], ep[606060], cu[606060 / 3], grau[606060 / 3];
char pos[606060];
vector<int> adj[606060 / 3], ed[606060 / 3];
void solve(int e) {
  if (tam[e] != -1) return;
  int v = ev[e], p = ep[e];
  tam[e] = 0;
  pos[e] = 1;
  int va = -1, vb = -1;
  for (int(i) = (0); (i) < (((int)(adj[v]).size())); (i)++)
    if (p != adj[v][i]) {
      int te = ed[v][i];
      solve(te);
      tam[e] = max(tam[e], tam[te] + 1);
      if (!pos[te]) pos[e] = 0;
      if (va == -1) va = tam[te];
      if (vb == -1 && tam[te] != va) vb = tam[te];
      if (va != tam[te] && vb != tam[te]) pos[e] = 0;
    }
  if (pos[e] && vb != -1) {
    if (v == p)
      tam[e] = va + vb + 2;
    else
      pos[e] = 0;
  }
}
int main() {
  memset(tam, -1, sizeof(tam));
  for (int(i) = (1); (i) < (606060 / 3); (i)++)
    if (!cu[i]) {
      cu[i] = i;
      int j = i << 1;
      while (j < 606060 / 3) {
        cu[j] = i;
        j <<= 1;
      }
    }
  scanf("%d", &n);
  for (int(i) = (0); (i) < (n); (i)++) ev[i] = ep[i] = i;
  for (int(i) = (0); (i) < (n - 1); (i)++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--, v--;
    adj[u].push_back(v);
    adj[v].push_back(u);
    ev[n + 2 * i] = v, ep[n + 2 * i] = u;
    ed[u].push_back(n + 2 * i);
    ev[n + 2 * i + 1] = u, ep[n + 2 * i + 1] = v;
    ed[v].push_back(n + 2 * i + 1);
    grau[u]++, grau[v]++;
  }
  int ans = 1e9;
  int c[2], pr = 0;
  queue<int> fila;
  for (int(i) = (0); (i) < (n); (i)++)
    if (grau[i] == 1) fila.push(i);
  while (!fila.empty()) {
    int v = fila.front();
    fila.pop();
    c[pr] = v;
    pr ^= 1;
    for (int(i) = (0); (i) < (((int)(adj[v]).size())); (i)++) {
      grau[adj[v][i]]--;
      if (grau[adj[v][i]] == 1) fila.push(adj[v][i]);
    }
  }
  for (int(i) = (0); (i) < (2); (i)++) {
    solve(c[i]);
    if (pos[c[i]]) ans = min(ans, cu[tam[c[i]]]);
  }
  if (ans > 1e7) ans = -1;
  printf("%d\n", ans);
}
