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, u, v, cnt[200100], dep[200100], root, ans, len[200100], tot, a[200100],
    son[200100];
bool flag[200100];
struct edge {
  int v;
  edge *nxt;
} pool[400100], *tp = pool, *fst[200100];
int getint() {
  char ch;
  while (!isdigit(ch = getchar()))
    ;
  int x = ch - '0';
  for (; isdigit(ch = getchar()); x = x * 10 + ch - '0')
    ;
  return x;
}
int cmp(int x, int y) { return len[x] < len[y]; }
void dfs1(int x, int fa) {
  dep[x] = dep[fa] + 1, tot = 0;
  for (edge *i = fst[x]; i; i = i->nxt)
    if (i->v != fa) {
      dfs1(i->v, x);
      if (len[i->v]) a[++tot] = i->v;
    }
  sort(a + 1, a + 1 + tot, cmp);
  for (int i = 2; i <= tot; ++i)
    if (len[a[i]] == len[a[i - 1]]) flag[a[i]] = 1;
  for (edge *i = fst[x]; i; i = i->nxt)
    if (i->v != fa && !flag[i->v])
      if (len[i->v] && !len[x])
        len[x] = len[i->v];
      else
        len[x] = -1;
  ++len[x];
}
void dfs2(int x, int fa) {
  if (len[x]) {
    ans = len[x] + dep[x] - 1;
    return;
  }
  for (edge *i = fst[x]; i; i = i->nxt)
    if (i->v != fa && !flag[i->v])
      if (!len[i->v] || len[i->v] != dep[x] - 1) {
        if (son[x]) {
          puts("-1");
          exit(0);
        }
        son[x] = i->v;
      } else
        flag[i->v] = 1;
  dfs2(son[x], x);
}
int main() {
  n = getint();
  for (int i = 1; i <= n - 1; ++i) {
    ++cnt[u = getint()], ++cnt[v = getint()];
    *tp = (edge){v, fst[u]}, fst[u] = tp++;
    *tp = (edge){u, fst[v]}, fst[v] = tp++;
  }
  for (int i = 1; i <= n; ++i)
    if (cnt[i] == 1) root = i;
  dfs1(root, 0);
  dfs2(root, 0);
  for (; ans & 1; ans = (ans + 1) / 2)
    ;
  printf("%d\n", ans - 1);
  return 0;
}
