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 rint() {
  int x = 0, f = 1;
  char ch = getchar();
  while ((ch < '0' || ch > '9') && (ch != '-')) ch = getchar();
  if (ch == '-') f = -1, ch = getchar();
  while (ch >= '0' && ch <= '9') x = x * 10 + ch - '0', ch = getchar();
  return f * x;
}
void juege() {
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
}
struct Edge {
  int son[400005], nxt[400005], lnk[200005], tot;
  void add(int x, int y) {
    tot++;
    son[tot] = y;
    nxt[tot] = lnk[x];
    lnk[x] = tot;
    tot++;
    son[tot] = x;
    nxt[tot] = lnk[y];
    lnk[y] = tot;
  }
} edge;
int R, n, ans;
int ask(int x, int pre) {
  int L = -1;
  for (int j = edge.lnk[x]; j; j = edge.nxt[j])
    if (edge.son[j] != pre) {
      int now = ask(edge.son[j], x);
      if (L == -1) {
        L = now;
        continue;
      }
      if (L != now) {
        if (pre != 0) {
          printf("%d\n", -1);
          exit(0);
        }
        if (R == -1) {
          R = now;
          continue;
        }
        if (R != now) {
          printf("%d\n", -1);
          exit(0);
        }
      }
    }
  if (!pre) {
    int ans = R + L + 2;
    if (!(ans % 2)) {
      while (ans) {
        ans >>= 1;
        if (!(ans % 2)) break;
      }
    }
    printf("%d\n", ans);
    exit(0);
  }
  L++;
  return L;
}
int dfs(int x, int pre) {
  int L = -1;
  for (int j = edge.lnk[x]; j; j = edge.nxt[j])
    if (edge.son[j] != pre) {
      int now = dfs(edge.son[j], x);
      if (L == -1) {
        L = now;
        continue;
      }
      if (L != now) ask(x, 0);
    }
  if (pre == 0) ask(x, 0);
  L++;
  return L;
}
int main() {
  n = rint(), R = -1;
  for (int i = (1); i < (n); i++) edge.add(rint(), rint());
  ans = dfs(1, 0);
  return 0;
}
