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 max_n = 202222, inf = 1011111111;
int n, was, dp[max_n], dp2[max_n], ans = inf;
vector<int> g[max_n], all[max_n];
void wa() {
  printf("-1\n");
  exit(0);
}
void dfs(int v, int p) {
  for (int i = 0; i < g[v].size(); ++i) {
    int to = g[v][i];
    if (to != p) {
      dfs(to, v);
      for (int j = 0; j < all[to].size(); ++j) {
        all[v].push_back(all[to][j] + 1);
      }
    }
  }
  if (all[v].size() == 0) {
    all[v].push_back(0);
  }
  sort(all[v].begin(), all[v].end());
  all[v].erase(unique(all[v].begin(), all[v].end()), all[v].end());
  if (all[v].size() > 2) {
    wa();
  }
  while (all[v].size() == 2 && all[v][0] % 2 == all[v][1] % 2) {
    int len = (all[v][1] - all[v][0]) / 2;
    all[v].pop_back();
    if (len) {
      all[v].push_back(len);
    }
  }
  for (int i = 0; i < all[v].size(); ++i) {
    dp[v] += all[v][i];
  }
}
void dfs2(int v, int p) {
  sort(all[v].begin(), all[v].end());
  all[v].erase(unique(all[v].begin(), all[v].end()), all[v].end());
  if (all[v].size() > 2) {
    return;
  }
  dp2[v] = 0;
  for (int i = 0; i < all[v].size(); ++i) {
    dp2[v] += all[v][i];
  }
  ans = min(ans, dp2[v]);
  multiset<int> q;
  for (int i = 0; i < g[v].size(); ++i) {
    int to = g[v][i];
    if (to != p) {
      for (int j = 0; j < all[to].size(); ++j) {
        q.insert(all[to][j]);
      }
    }
  }
  for (int i = 0; i < g[v].size(); ++i) {
    int to = g[v][i];
    if (to != p) {
      vector<int> er;
      for (int j = 0; j < all[to].size(); ++j) {
        er.push_back(all[to][j]);
        q.erase(q.find(all[to][j]));
      }
      if (er.size() == all[v].size()) {
        all[to].push_back(1);
      }
      int mn = -1;
      while (q.size()) {
        multiset<int>::iterator it = q.upper_bound(mn);
        if (it != q.end()) {
          mn = *it;
          all[to].push_back(mn);
        }
      }
      dfs2(to, v);
      for (int j = 0; j < er.size(); ++j) {
        q.insert(er[j]);
      }
    }
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    g[u].push_back(v);
    g[v].push_back(u);
  }
  for (int i = 1; i <= n; ++i) {
    dp2[i] = inf;
  }
  dfs(1, -1);
  dfs2(1, -1);
  if (ans == inf) {
    ans = -1;
  }
  printf("%d\n", ans);
  return 0;
}
