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 kN = 2e5 + 10;
int N;
vector<int> G[kN];
int ans = -1;
int root = -1;
int dfs_root;
int dfs(int u, int fa) {
  vector<int> down;
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v != fa) {
      int s_l = dfs(v, u);
      if (s_l == -1) return -1;
      down.push_back(s_l);
    }
  }
  int rem1 = 0, rem2 = 0;
  sort(down.begin(), down.end());
  for (int i = 0; i < down.size(); i++) {
    if (rem1 == down[i]) {
      continue;
    }
    if (rem2 == down[i]) {
      continue;
    }
    if (i == down.size() - 1) {
      if (!rem1)
        rem1 = down[i];
      else if (!rem2)
        rem2 = down[i];
      else
        return -1;
    } else {
      int l1 = down[i];
      int l2 = down[i + 1];
      if (l1 == l2) {
        i++;
      }
      if (!rem1)
        rem1 = down[i];
      else if (!rem2)
        rem2 = down[i];
      else
        return -1;
    }
  }
  if (u == dfs_root) {
    ans = rem1 + rem2;
    if (ans % 2 == 0) ans = 0;
    return ans;
  } else {
    if (rem2 == 0)
      return rem1 + 1;
    else {
      root = u;
      return -1;
    }
  }
}
int main() {
  scanf("%d", &N);
  for (int i = 1; i <= N - 1; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  dfs_root = 1;
  int ret = dfs(1, 0);
  if (ret == -1 && root != -1) {
    dfs_root = root;
    dfs(dfs_root, 0);
  }
  printf("%d\n", ans);
  return 0;
}
