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 maxn = 200050;
struct node {
  int to, next;
} e[maxn * 2];
int n, m, head[maxn], tot, size[maxn], rt, mx, up[maxn], ch, len, len1, len2;
void insert(int u, int v) {
  e[++tot].to = v;
  e[tot].next = head[u];
  head[u] = tot;
}
void dfs(int u, int f) {
  size[u] = 1;
  int sz = 0;
  for (int i = head[u]; i; i = e[i].next) {
    int v = e[i].to;
    if (v == f) continue;
    dfs(v, u);
    size[u] += size[v];
    sz = max(sz, size[v]);
  }
  sz = max(sz, n - size[u]);
  if (sz < mx) mx = sz, rt = u;
}
void work(int u, int f) {
  up[u] = 0;
  for (int i = head[u]; i; i = e[i].next) {
    int v = e[i].to;
    if (v == f) continue;
    work(v, u);
    if (up[v] == 1000000010) up[u] = 1000000010;
    if (u != rt) {
      if (up[v] == 1000000010)
        up[u] = 1000000010;
      else if (!up[u])
        up[u] = up[v] + 1;
      else if (up[u] != up[v] + 1 && u != rt)
        up[u] = 1000000010;
    }
  }
  if (!up[u]) up[u] = 1;
}
int main() {
  scanf("%d", &n);
  mx = 1000000010;
  for (int i = 1, u, v; i < n; i++)
    scanf("%d%d", &u, &v), insert(u, v), insert(v, u);
  dfs(1, 0);
  work(rt, 0);
  if (up[rt] == 1000000010) {
    puts("-1");
    return 0;
  }
  for (int i = head[rt]; i; i = e[i].next) ch++;
  if (ch == 2) {
    len = 0;
    for (int i = head[rt]; i; i = e[i].next) {
      int v = e[i].to;
      len += up[v];
    }
    while (len & 1) {
      len = (len + 1) >> 1;
    }
    printf("%d\n", len - 1);
  } else {
    len1 = len2 = 0;
    for (int i = head[rt]; i; i = e[i].next) {
      int v = e[i].to;
      if (!len1)
        len1 = up[v];
      else if (!len2 && len1 != up[v])
        len2 = up[v];
      else if (up[v] != len1 && up[v] != len2) {
        puts("-1");
        return 0;
      }
    }
    len = len1 + len2 + 1;
    while (len & 1) len = (len + 1) >> 1;
    printf("%d\n", len - 1);
  }
  return 0;
}
