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 int read() {
  int x;
  char c;
  while ((c = getchar()) < '0' || c > '9')
    ;
  for (x = c - '0'; (c = getchar()) >= '0' && c <= '9';)
    x = (x << 3) + (x << 1) + c - '0';
  return x;
}
struct edge {
  int nx, t;
} e[200000 * 2 + 5];
int h[200000 + 5], en, d[200000 + 5], d1[200000 + 5], d2[200000 + 5],
    c[200000 + 5], g;
inline void ins(int x, int y) {
  e[++en] = (edge){h[x], y};
  h[x] = en;
  e[++en] = (edge){h[y], x};
  h[y] = en;
}
void cal(int x, int d) {
  if (!d1[x])
    d1[x] = d;
  else if (d1[x] != d)
    if (!d2[x])
      d2[x] = d;
    else if (d2[x] != d)
      g = 1;
}
void pre(int x, int f) {
  for (int i = h[x]; i; i = e[i].nx)
    if (e[i].t != f) {
      pre(e[i].t, x);
      if (d[e[i].t] >= d[x])
        c[x] = d[x], d[x] = d[e[i].t];
      else if (d[e[i].t] > c[x])
        c[x] = d[e[i].t];
      cal(x, d[e[i].t]);
    }
  ++d[x];
  ++c[x];
}
void dfs(int x, int f, int fd) {
  if (f) cal(x, fd);
  for (int i = h[x]; i; i = e[i].nx)
    if (e[i].t != f)
      dfs(e[i].t, x, max(fd + 1, d[x] == d[e[i].t] + 1 ? c[x] : d[x]));
}
int main() {
  int n = read(), i, ans;
  for (i = 1; i < n; ++i) ins(read(), read());
  pre(1, 0);
  dfs(1, 0, 0);
  if (g) return 0 * puts("-1");
  for (ans = d1[1] + d2[1], i = 2; i <= n; ++i) ans = min(ans, d1[i] + d2[i]);
  while (ans % 2 == 0) ans /= 2;
  printf("%d", ans);
}
