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;
int N;
vector<int> E[201010];
int len[201010];
int can[201010];
void dfs1(int cu, int pa = 0) {
  len[cu] = 1;
  can[cu] = 1;
  set<int> lens;
  for (int to : E[cu])
    if (to != pa) {
      dfs1(to, cu);
      if (can[to] == 0) can[cu] = 0;
      lens.insert(len[to] + 1);
    }
  if (1 < lens.size())
    can[cu] = 0;
  else if (lens.size() == 1)
    len[cu] = *lens.begin();
}
int ans = INT_MAX / 2;
void dfs2(int cu, int pa = 0) {
  map<int, int> lens;
  int cans[2] = {0};
  for (int to : E[cu]) {
    cans[can[to]]++;
    lens[len[to]]++;
  }
  if (cans[0] == 0 && lens.size() <= 2) {
    if (E[cu].size() == 1)
      ans = min(ans, len[E[cu][0]]);
    else if (lens.size() == 1)
      ans = min(ans, len[E[cu][0]]);
    else if (lens.size() == 2) {
      int sm = 0;
      for (auto p : lens) sm += p.first;
      ans = min(ans, sm);
    }
  }
  int bcan = can[cu];
  int blen = len[cu];
  if (cans[0] == 0 && lens.size() == 1) {
    can[cu] = true;
    len[cu] = len[E[cu][0]] + 1;
    for (int to : E[cu])
      if (to != pa) dfs2(to, cu);
  } else if (cans[0] == 0 && lens.size() == 2) {
    int sm = 0;
    vector<int> alen;
    for (auto p : lens) {
      sm += p.first;
      if (p.second == 1) alen.push_back(p.first);
    }
    for (int to : E[cu])
      if (to != pa) {
        bool ok = false;
        for (int i : alen)
          if (i == len[to]) ok = true;
        if (ok) {
          can[cu] = true;
          len[cu] = sm - len[to] + 1;
          dfs2(to, cu);
        }
      }
  } else if (cans[0] == 1 && lens.size() == 1) {
    for (int to : E[cu])
      if (to != pa) {
        if (can[to] == 1) continue;
        can[cu] = true;
        len[cu] = len[to] + 1;
        dfs2(to, cu);
      }
  } else if (cans[0] == 1 && lens.size() == 2) {
    int sm = 0;
    vector<int> alen;
    for (auto p : lens) {
      sm += p.first;
      if (p.second == 1) alen.push_back(p.first);
    }
    for (int to : E[cu])
      if (to != pa) {
        bool ok = false;
        if (can[to] == 1) continue;
        for (int i : alen)
          if (i == len[to]) ok = true;
        if (ok) {
          can[cu] = true;
          len[cu] = sm - len[to] + 1;
          dfs2(to, cu);
        }
      }
  }
}
int main() {
  cin >> N;
  for (int i = 0; i < N - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    E[a].push_back(b);
    E[b].push_back(a);
  }
  dfs1(1);
  dfs2(1);
  if (ans == INT_MAX / 2) ans = -1;
  cout << ans << endl;
}
