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 N = 200010;
struct edge {
  int to, pre;
} e[N << 1];
int u[N], l = 1;
void ins(int a, int b) { e[++l] = (edge){b, u[a]}, u[a] = l; }
int n, f[N << 1];
bool vis[N << 1];
void upd(int &a, int b) {
  if (b == -1) return;
  if (a == -1 || b < a) a = b;
}
int b[N];
void dp(int t) {
  if (vis[t]) return;
  int x = e[t].to;
  vis[t] = true;
  int l = 0;
  for (int i = u[x]; i; i = e[i].pre)
    if (i ^ t ^ 1) dp(i);
  for (int i = u[x]; i; i = e[i].pre)
    if (i ^ t ^ 1) b[++l] = f[i];
  if (l) {
    sort(b + 1, b + l + 1);
    l = unique(b + 1, b + l + 1) - b - 1;
  }
  if (!l)
    f[t] = 1;
  else if (l > 1 || b[1] == -1)
    f[t] = -1;
  else
    f[t] = b[1] + 1;
}
int calc(int x) {
  int l = 0;
  for (int i = u[x]; i; i = e[i].pre) dp(i);
  for (int i = u[x]; i; i = e[i].pre) b[++l] = f[i];
  if (l) {
    sort(b + 1, b + l + 1);
    l = unique(b + 1, b + l + 1) - b - 1;
  }
  if (l > 2 || b[1] == -1)
    return -1;
  else {
    b[l + 1] = b[l + 2] = 0;
    return b[1] + b[2];
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    ins(a, b), ins(b, a);
  }
  int ans = -1;
  for (int i = 1; i <= n; i++) upd(ans, calc(i));
  cout << ans << endl;
  return 0;
}
