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;
inline char gc() {
  static char buf[100000], *p1 = buf, *p2 = buf;
  return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 100000, stdin), p1 == p2)
             ? EOF
             : *p1++;
}
inline int read() {
  char c = getchar();
  int tot = 1;
  while ((c < '0' || c > '9') && c != '-') c = getchar();
  if (c == '-') {
    tot = -1;
    c = getchar();
  }
  int sum = 0;
  while (c >= '0' && c <= '9') {
    sum = sum * 10 + c - '0';
    c = getchar();
  }
  return sum * tot;
}
inline void wr(int x) {
  if (x < 0) {
    putchar('-');
    wr(-x);
    return;
  }
  if (x >= 10) wr(x / 10);
  putchar(x % 10 + '0');
}
inline void wrn(int x) {
  wr(x);
  putchar('\n');
}
inline void wri(int x) {
  wr(x);
  putchar(' ');
}
inline void wrn(int x, int y) {
  wri(x);
  wrn(y);
}
inline void wrn(int a, int b, int c) {
  wri(a);
  wrn(b, c);
}
int n, m, fa[500055], dis[500055], g[500055], u, v, lon, rt;
int nedge, Next[500055 * 2], head[500055], to[500055 * 2];
void add(int a, int b) {
  Next[++nedge] = head[a];
  head[a] = nedge;
  to[nedge] = b;
}
void add_ne(int a, int b) {
  add(a, b);
  add(b, a);
}
void dfs(int x, int y) {
  if (dis[x] > dis[u]) u = x;
  for (int i = head[x]; i; i = Next[i]) {
    if (to[i] == y) continue;
    dis[to[i]] = dis[x] + 1;
    fa[to[i]] = x;
    dfs(to[i], x);
  }
}
void ret() {
  puts("-1");
  exit(0);
}
void dfs2(int x) {
  int q = 0, p = 0;
  for (int i = head[x]; i; i = Next[i]) {
    if (to[i] == fa[x]) continue;
    fa[to[i]] = x;
    dfs2(to[i]);
    if (q == 0) q = g[to[i]];
    if (q != g[to[i]]) {
      if (x == rt) {
        if (p == 0) p = g[to[i]];
        if (p != g[to[i]]) ret();
      } else
        ret();
    }
  }
  g[x] = q + 1;
  if (x == rt && p > 0) g[x] = q + p + 1;
}
signed main() {
  n = read();
  for (int i = (1); i <= (n - 1); i++) add_ne(read(), read());
  dfs(1, 0);
  v = u;
  u = 0;
  dis[v] = 0;
  dfs(v, 0);
  lon = dis[u];
  for (int i = u, j = 0; j <= lon; j += 2, i = fa[i]) rt = i;
  fa[rt] = 0;
  dfs2(rt);
  int t = g[rt];
  while ((t & 1) && t > 1) t = t / 2 + 1;
  wrn(t - 1);
  return 0;
}
