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<vector<int> > adj;
vector<vector<int> > chd;
vector<int> par;
void dfs(int u, int p) {
  for (int i = 0; i < adj[u].size(); i++) {
    int v = adj[u][i];
    if (v == p) continue;
    dfs(v, u);
    chd[u].push_back(v);
    par[v] = u;
  }
}
int dp(int u);
int dp2(int u, int c);
int dp3(int u);
vector<int> cc;
int dp(int u) {
  int &ret = cc[u];
  if (ret != -1) return ret;
  set<int> st;
  int cnt = 0;
  int len = 0;
  for (int i = 0; i < chd[u].size(); i++) {
    int t = 1 + dp(chd[u][i]);
    if (t == -1) return ret = -2;
    if (st.find(t) == st.end()) {
      st.insert(t);
      cnt++;
      len += t;
    }
  }
  if (cnt > 1)
    return ret = -2;
  else
    return ret = len;
}
vector<vector<int> > cc2;
int dp2(int u, int c) {
  int &ret = cc2[u][c];
  if (ret != -1) return ret;
  set<int> st;
  int cnt = 0;
  int len = 0;
  for (int i = 0; i < chd[u].size(); i++) {
    if (i == c) continue;
    int t = 1 + dp(chd[u][i]);
    if (t == -1) return ret = -2;
    if (st.find(t) == st.end()) {
      st.insert(t);
      cnt++;
      len += t;
    }
  }
  if (par[u] != -1) {
    int t = 1 + dp3(par[u]);
    if (t == -1) return ret = -2;
    if (st.find(t) == st.end()) {
      st.insert(t);
      cnt++;
      len += t;
    }
  }
  if (cnt > 1)
    return ret = -2;
  else
    return ret = len;
}
vector<int> cc3;
int dp3(int u) {
  int &ret = cc3[u];
  if (ret != -1) return ret;
  if (par[u] == -1)
    return -2;
  else {
    int v = par[u];
    int c;
    for (int i = 0; i < chd[v].size(); i++) {
      if (chd[v][i] == u) {
        c = i;
        break;
      }
    }
    return ret = dp2(v, c);
  }
}
int main() {
  scanf("%d", &N);
  adj.resize(N);
  for (int i = 0; i < N - 1; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    u--;
    v--;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  chd.resize(N);
  par = vector<int>(N, -1);
  dfs(0, -1);
  cc = vector<int>(N, -1);
  cc2.resize(N);
  for (int i = 0; i < N; i++) {
    cc2[i] = vector<int>(chd[i].size(), -1);
  }
  cc3 = vector<int>(N, -1);
  int ans = 1e9;
  for (int i = 0; i < N; i++) {
    if (i == 0 && dp(i) != -2) ans = min(ans, dp(i));
    for (int j = 0; j < chd[i].size(); j++) {
      int k = chd[i][j];
      if (dp2(i, j) != -2 && dp(k) != -2) {
        ans = min(ans, dp(k) + 1 + dp2(i, j));
      }
    }
  }
  if (ans == 1e9)
    printf("-1");
  else
    printf("%d", ans);
}
