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 MAXN = 200000 + 1;
const int INF = INT_MAX;
vector<int> p[MAXN];
int n, u, v;
map<pair<int, int>, int> dp;
int top;
int cal(int a, int b) {
  pair<int, int> e = make_pair(a, b);
  if (dp.count(e)) return dp[e];
  if (p[b].size() == 1 && a) {
    dp[e] = 0;
  } else {
    set<int> s;
    for (int i = 0; i < p[b].size(); i++) {
      if (p[b][i] != a) s.insert(cal(b, p[b][i]));
    }
    set<int>::iterator it = s.begin();
    if (a) {
      if (s.size() == 1 && *it != INF)
        dp[e] = *it + 1;
      else
        dp[e] = INF;
    } else {
      if (s.size() <= 2) {
        int tmp = 0;
        for (; it != s.end(); it++) {
          if (*it == INF) {
            tmp = INF;
          } else
            tmp += *it + 1;
        }
        dp[e] = tmp;
      } else
        dp[e] = INF;
    }
  }
  return dp[e];
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    scanf("%d%d", &u, &v);
    p[u].push_back(v);
    p[v].push_back(u);
  }
  int res = INF;
  top = 0;
  for (int i = 1; i <= n; i++) {
    int dpi = cal(0, i);
    res = min(res, dpi);
  }
  printf("%d\n", res == INF ? -1 : res);
}
