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 = 200010;
const int INF = 0x3f3f3f3f;
vector<int> adj[N];
set<int> dp[N];
int ok;
void dfs(int u, int v = -1) {
  if (adj[u].size() == 1) {
    dp[u].insert(0);
    return;
  }
  for (int i = 0; i < adj[u].size(); i++) {
    if (adj[u][i] == v) continue;
    dfs(adj[u][i], u);
    for (auto it : dp[adj[u][i]]) {
      dp[u].insert(it + 1);
    }
    if (dp[u].size() > 2) {
      ok = 0;
      return;
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    a--, b--;
    adj[a].push_back(b);
    adj[b].push_back(a);
  }
  int raiz = 0;
  for (int i = 0; i < n; i++) {
    if (adj[i].size() == 1) raiz = i;
  }
  int pivot;
  int last = raiz;
  for (pivot = adj[raiz][0]; adj[pivot].size() < 3;) {
    if (adj[pivot].size() == 1) {
      pivot = -1;
      break;
    } else {
      if (last == adj[pivot][0]) {
        last = pivot;
        pivot = adj[pivot][1];
      } else if (last == adj[pivot][1]) {
        last = pivot;
        pivot = adj[pivot][0];
      }
    }
  }
  ok = 1;
  if (pivot == -1) {
    printf("%d\n", n - 1);
  } else {
    dfs(pivot);
    if (ok) {
      auto it = dp[pivot].begin();
      int ans = *it;
      it++;
      ans += *it;
      printf("%d\n", ans);
    } else
      printf("%d\n", -1);
  }
  return 0;
}
