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;
set<int> G[200005];
int st[200005], n, ans;
bool deuruim;
int val[2], qual_ponta, diametro, ponta[2];
int dist[2][200005];
void dia(int v, int p, int d) {
  diametro = max(diametro, d);
  if (d > val[qual_ponta]) {
    val[qual_ponta] = d;
    ponta[qual_ponta] = v;
  }
  for (int u : G[v]) {
    if (p != u) dia(u, v, d + 1);
  }
}
void dia2(int v, int p, int d, int tp) {
  dist[tp][v] = d;
  for (int u : G[v]) {
    if (p != u) dia2(u, v, d + 1, tp);
  }
}
void calc(int v, int p) {
  st[v] = 1;
  for (int x : G[v]) {
    if (x != p) {
      calc(x, v);
      st[v] += st[x];
    }
  }
}
bool dfs(int v, int p) {
  int filhos = 0;
  bool flag = 0;
  map<int, vector<int> > tab;
  st[v] = 1;
  for (int x : G[v]) {
    if (x == p) continue;
    filhos++;
    bool aux = dfs(x, v);
    flag |= aux;
    st[v] += st[x];
    if (!aux) {
      tab[st[x]].push_back(x);
    }
  }
  for (auto &it : tab) {
    while ((it.second).size() > 1) {
      G[v].erase((it.second).back());
      st[v] -= st[(it.second).back()];
      filhos--;
      (it.second).pop_back();
    }
  }
  return flag | (filhos >= 2);
}
void check(int v, int p) {
  ans++;
  if (G[v].size() > 2) deuruim = 1;
  for (int x : G[v])
    if (x != p) check(x, v);
}
int main() {
  int a, b;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    scanf("%d%d", &a, &b);
    G[a].insert(b);
    G[b].insert(a);
  }
  diametro = 0;
  val[0] = val[1] = -1;
  qual_ponta = 0;
  dia(1, 0, 0);
  qual_ponta = 1;
  dia(ponta[0], 0, 0);
  dia2(ponta[0], 0, 0, 0);
  dia2(ponta[1], 0, 0, 1);
  int root = -1;
  for (int i = 1; i <= n; i++) {
    if ((diametro + 1) / 2 >= dist[0][i] && (diametro + 1) / 2 >= dist[1][i])
      root = i;
  }
  dfs(root, root);
  ans = 0;
  check(root, root);
  if (deuruim)
    printf("-1\n");
  else {
    ans--;
    while (ans && ans % 2 == 0) ans /= 2;
    printf("%d\n", ans);
  }
  return 0;
}
