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 MOD = 1000000007;
const int N = 200010;
struct Edge {
  int to, nxt;
} e[N << 1];
int cnt, lst[N], dep[N], s1, s2, s3, cha[N];
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (!isdigit(ch) && ch != '-') ch = getchar();
  if (ch == '-') f = -1, ch = getchar();
  while (isdigit(ch)) {
    x = (x << 1) + (x << 3) + (ch ^ 48);
    ch = getchar();
  }
  return x * f;
}
inline void add(int u, int v) {
  e[++cnt].to = v;
  e[cnt].nxt = lst[u];
  lst[u] = cnt;
}
inline void dfs(int x, int fa) {
  dep[x] = dep[fa] + 1;
  for (int i = lst[x]; i; i = e[i].nxt) {
    int son = e[i].to;
    if (son == fa) continue;
    dfs(son, x);
  }
}
inline int dfs1(int x, int fa) {
  if (x == s2) return 1;
  for (int i = lst[x]; i; i = e[i].nxt) {
    int son = e[i].to;
    if (son == fa) continue;
    if (dfs1(son, x)) {
      if (dep[x] == dep[s2] / 2) s3 = x;
      return 1;
    }
  }
  return 0;
}
inline void dfs2(int x, int fa) {
  dep[x] = dep[fa] + 1;
  if (e[lst[x]].nxt == 0) cha[x] = dep[x];
  for (int i = lst[x]; i; i = e[i].nxt) {
    int son = e[i].to;
    if (son == fa) continue;
    dfs2(son, x);
    if (x == s3) continue;
    if (cha[son] == -1) {
      cha[x] = -1;
      return;
    }
    if (!cha[x])
      cha[x] = cha[son];
    else {
      if (cha[x] != cha[son]) {
        cha[x] = -1;
        return;
      }
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = (int)(1); i <= (int)(n - 1); ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    add(u, v);
    add(v, u);
  }
  dfs(1, 1);
  dep[1] = -1;
  s1 = 1;
  for (int i = (int)(2); i <= (int)(n); ++i) {
    if (dep[i] > dep[s1]) s1 = i;
  }
  memset(dep, 0, sizeof dep);
  dep[s1] = -1;
  dfs(s1, s1);
  s2 = s1;
  for (int i = (int)(1); i <= (int)(n); ++i) {
    if (dep[i] > dep[s2]) s2 = i;
  }
  dfs1(s1, s1);
  memset(dep, 0, sizeof dep);
  dep[s3] = -1;
  dfs2(s3, s3);
  int lt = 0, ltt = 0;
  for (int i = lst[s3]; i; i = e[i].nxt) {
    int son = e[i].to;
    if (cha[son] == -1) {
      puts("-1");
      return 0;
    }
    if (!lt)
      lt = cha[son];
    else if (cha[son] != lt) {
      if (!ltt) ltt = cha[son];
      if (cha[son] != ltt) {
        puts("-1");
        return 0;
      }
    }
  }
  int ans = lt + ltt;
  printf("%d\n", ans);
  while (!(ans & 1)) ans >>= 1;
  return 0;
}
