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 N = 2e5 + 5, M = 1e7 + 5, K = 25;
vector<int> g[N];
int in[N], out[N], timer, n;
pair<int, int> lazy[4 * N], seg[4 * N];
void prop(int node, int l, int r, pair<int, int> val) {
  if (val.first != 0) {
    seg[node] = {seg[node].first + val.first, seg[node].second + val.second};
    if (l != r) {
      lazy[node << 1] = {lazy[node << 1].first + val.first,
                         lazy[node << 1].second + val.second};
      lazy[node << 1 | 1] = {lazy[node << 1 | 1].first + val.first,
                             lazy[node << 1 | 1].second + val.second};
    }
    lazy[node] = {0, 0};
  }
}
void update(int node, int l, int r, int i, int j, pair<int, int> val,
            bool bo = 1) {
  prop(node, l, r, lazy[node]);
  if (l > j || r < i) return;
  if (l >= i && r <= j) {
    if (i == j && bo) {
      if (val.first == -2) {
        seg[node] = {1e9, -1e9};
      } else if (val.first == 2)
        seg[node] = {1, 1};
      return;
    }
    prop(node, l, r, val);
    return;
  }
  int md = l + r >> 1;
  update(node << 1, l, md, i, j, val, bo),
      update(node << 1 | 1, md + 1, r, i, j, val, bo);
  seg[node] = make_pair(min(seg[node << 1].first, seg[node << 1 | 1].first),
                        max(seg[node << 1].second, seg[node << 1 | 1].second));
}
void pre(int node, int parent, int depth) {
  in[node] = ++timer;
  if (g[node].size() == 1)
    update(1, 1, n, in[node], in[node], {depth, depth}, 0);
  else
    update(1, 1, n, in[node], in[node], {1e9, -1e9}, 0);
  for (auto child : g[node])
    if (child != parent) {
      pre(child, node, depth + 1);
    }
  out[node] = timer;
}
int mn = 1e9, ans;
void dfs(int node, int parent) {
  if (seg[1].second == seg[1].first) {
    if (seg[1].first < mn) {
      mn = seg[1].first;
      ans = node;
    } else if (seg[1].first == mn) {
      if (node < ans) ans = node;
    }
  }
  for (auto child : g[node])
    if (child != parent) {
      update(1, 1, n, 1, n, {1, 1});
      update(1, 1, n, in[child], out[child], {-2, -2});
      dfs(child, node);
      update(1, 1, n, 1, n, {-1, -1});
      update(1, 1, n, in[child], out[child], {2, 2});
    }
}
int root = -1;
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  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);
    if (g[x].size() == 2) root = x;
    if (g[y].size() == 2) root = y;
  }
  if (root == -1) return cout << "1", 0;
  pre(root, root, 0);
  dfs(root, root);
  if (mn == 1e9) return cout << -1, 0;
  cout << mn;
  return 0;
}
