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;
vector<int> tree[200005];
int dist[200005], n;
bool vis[200005];
void dfs(int now, int d) {
  vis[now] = true;
  dist[now] = d;
  for (int i = 0; i < tree[now].size(); i++) {
    int to = tree[now][i];
    if (vis[to]) continue;
    dfs(to, d + 1);
  }
}
pair<int, int> go(int now) {
  vis[now] = true;
  set<int> second;
  pair<int, int> t;
  for (int i = 0; i < tree[now].size(); i++) {
    int to = tree[now][i];
    if (vis[to]) continue;
    t = go(to);
    if (t.first == -1) {
      return t;
    }
    if (t.first == 0) {
      return make_pair(-1, -1);
    }
    second.insert(t.second);
  }
  if (second.size() == 0) {
    return make_pair(1, 1);
  }
  if (second.size() == 1) {
    set<int>::iterator it = second.begin();
    return make_pair(1, *it + 1);
  }
  if (second.size() == 2) {
    int ans = 0;
    set<int>::iterator it = second.begin();
    while (it != second.end()) {
      ans += *it;
      it++;
    }
    return make_pair(0, ans);
  }
  return make_pair(-1, -1);
}
int main() {
  int i, j;
  scanf("%d", &n);
  for (i = 1; i < n; i++) {
    int u, v;
    scanf("%d", &u);
    scanf("%d", &v);
    tree[u].push_back(v);
    tree[v].push_back(u);
  }
  memset(vis, false, sizeof(vis));
  dfs(1, 0);
  int t = -1, node;
  for (i = 1; i <= n; i++) {
    if (dist[i] > t) {
      t = dist[i];
      node = i;
    }
  }
  memset(vis, false, sizeof(vis));
  dfs(node, 0);
  t = -1;
  for (i = 1; i <= n; i++) t = max(t, dist[i]);
  t /= 2;
  for (i = 1; i <= n; i++)
    if (dist[i] == t) {
      node = i;
      break;
    }
  memset(vis, false, sizeof(vis));
  pair<int, int> p = go(node);
  if (p.first == -1)
    printf("-1\n");
  else if (p.first == 0) {
    if (p.second % 2 == 0) p.second = 1;
    printf("%d\n", p.second);
  } else {
    if ((p.second - 1) % 2 == 0) p.second = 1;
    printf("%d\n", p.second - 1);
  }
  return 0;
}
