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 N = 800100;
struct node {
  int ne, to;
} e[N];
int f[N], h[N], h1[N], h2[N], n, he[N], tot = 0, to[N];
void add(int x, int y) {
  e[++tot].ne = he[x];
  he[x] = tot;
  e[tot].to = y;
}
void go() {
  printf("-1\n");
  exit(0);
}
void out(int x) {
  x--;
  while (x != 1) {
    if (x % 2 == 0)
      x /= 2;
    else
      break;
  }
  printf("%d\n", x);
  exit(0);
}
void dfs(int x, int fa) {
  int i, y, top1 = 0, top2 = 0;
  f[x] = 1;
  for (i = he[x]; i; i = e[i].ne)
    if ((y = e[i].to) != fa) {
      dfs(y, x);
      if ((!f[y]) && (top2)) go();
      if (!f[y]) {
        f[x] = 0;
        to[x] = y;
        top2++;
        continue;
      }
      if ((top1 == 2) && (h[y] + 1 != h1[x]) && (h[y] + 1 != h2[x])) go();
      if (!top1)
        h1[x] = h[y] + 1, top1++;
      else if ((top1 == 1) && (h1[x] != h[y] + 1))
        h2[x] = h[y] + 1, top1++;
    }
  if ((!top1) && (!top2))
    h[x] = 0;
  else if ((!top2) && (top1 == 1))
    h[x] = h1[x];
  if (top1 == 2) f[x] = 0;
}
void dfs2(int x, int fa, int dep) {
  if (!to[x]) {
    if (!h2[x])
      out(h[x] + dep + 1);
    else if (h1[x] == dep)
      out(h2[x] + dep + 1);
    else if (h2[x] == dep)
      out(h1[x] + dep + 1);
    else
      go();
  }
  if (h1[x] == -10000) dfs2(to[x], x, dep + 1);
  if (h1[x] == dep)
    dfs2(to[x], x, dep + 1);
  else if (x == 1)
    dfs2(to[x], x, h1[x] + 1);
  else
    go();
}
int main() {
  int i, j, k, x, y;
  scanf("%d", &n);
  for (i = 1; i < n; i++) {
    scanf("%d%d", &x, &y);
    add(x, y);
    add(y, x);
  }
  for (i = 1; i <= n; i++) h[i] = h1[i] = h2[i] = -10000;
  dfs(1, 0);
  dfs2(1, 0, 0);
  return 0;
}
