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;
const int maxi = 1e6 + 10;
vector<int> v[maxi];
int n;
int node, mm;
int d1[maxi], d2[maxi];
int ok = 1;
int dp[maxi];
int ans;
void dfs(int x, int pred, int lev) {
  if (lev > mm) {
    mm = lev;
    node = x;
  }
  for (int i : v[x])
    if (i != pred) dfs(i, x, lev + 1);
}
void dfs1(int x, int pred, int *d) {
  d[x] = d[pred] + 1;
  for (int i : v[x])
    if (i != pred) dfs1(i, x, d);
}
void dfs2(int x, int pred) {
  set<int> st;
  int mm = 0;
  for (int i : v[x])
    if (i != pred) {
      dfs2(i, x);
      mm = max(dp[i], mm);
      st.insert(dp[i]);
    }
  if (x == node && st.size() == 1) {
    ans = mm;
  } else if (x == node && st.size() == 2) {
    ans = *st.begin();
    st.erase(st.begin());
    ans += *st.begin();
    ans;
  } else if (x == node)
    ok = 0;
  else if (st.size() > 1)
    ok = 0;
  dp[x] = mm + 1;
}
int main() {
  cin >> n;
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    v[x].push_back(y);
    v[y].push_back(x);
  }
  node = -1;
  mm = 0;
  dfs(1, 0, 1);
  int node1 = node;
  mm = -1;
  node = 0;
  dfs(node1, 0, 0);
  int node2 = node;
  d1[0] = -1;
  d2[0] = -1;
  dfs1(node1, 0, d1);
  dfs1(node2, 0, d2);
  for (int i = 1; i <= n; i++)
    if (d1[i] + d2[i] == mm && d1[i] == mm / 2) node = i;
  dfs2(node, 0);
  if (!ok)
    return !printf("-1\n");
  else {
    while (ans % 2 == 0) ans /= 2;
    return !printf("%d\n", ans);
  }
}
