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> g[200010];
int ch[200010];
int ret = 300000;
multiset<int> tc[200010];
set<int> vr[200010];
int aj[200010];
void pre(int v, int p) {
  ch[v] = -1;
  int u = -1;
  for (int to : g[v])
    if (to != p) {
      pre(to, v);
      aj[v]++;
      if (ch[to] != -1) {
        tc[v].insert(ch[to] + 1);
        vr[v].insert(ch[to] + 1);
        if (u == -1) {
          u = ch[to] + 1;
        } else {
          if (u != ch[to] + 1) {
            u = -2;
          }
        }
      } else {
        u = -2;
      }
    }
  if (u == -1)
    ch[v] = 0;
  else if (u > 0)
    ch[v] = u;
}
void calc(int v, int p, int chp) {
  if (p == -1) {
    if (tc[v].size() == aj[v] && vr[v].size() <= 2) {
      int u = 0;
      for (const int x : vr[v]) {
        u += x;
      }
      ret = min(ret, u);
    }
  } else {
    if (tc[v].size() == aj[v] && vr[v].size() <= 2 && chp != -2) {
      set<int> ss;
      for (const int x : vr[v]) {
        ss.insert(x);
      }
      ss.insert(chp);
      if (ss.size() <= 2) {
        int u = 0;
        for (const int x : ss) {
          u += x;
        }
        ret = min(ret, u);
      }
    }
  }
  for (int to : g[v])
    if (to != p) {
      int x = ch[to] + 1;
      bool f = ch[to] != -1;
      if (f) {
        tc[v].erase(tc[v].lower_bound(x));
        if (!tc[v].count(x)) {
          vr[v].erase(x);
        }
      }
      int nc = chp;
      if (chp != -2) {
        if (vr[v].size() >= 2 || (int)tc[v].size() != aj[v] - 1) {
          nc = -2;
        } else {
          if (tc[v].size()) {
            if (chp == -1) {
              nc = *tc[v].begin() + 1;
            } else {
              if (chp != *tc[v].begin()) {
                nc = -2;
              } else {
                nc = chp + 1;
              }
            }
          } else {
            if (chp == -1) {
              nc = 1;
            } else
              ++nc;
          }
        }
      }
      calc(to, v, nc);
      if (f) {
        tc[v].insert(x);
        vr[v].insert(x);
      }
    }
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < (n - 1); i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    --a;
    --b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  for (int t = 0; t < (20); t++) {
    for (int i = 0; i < (n); i++) {
      tc[i].clear();
      vr[i].clear();
    }
    int rt = abs(rand()) % n;
    pre(rt, -1);
    calc(rt, -1, -1);
  }
  if (ret == 300000) ret = -1;
  printf("%d\n", ret);
  return 0;
}
