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 maxn = 2e5;
vector<int> g[maxn];
int d[maxn], vis[maxn];
int len[maxn][2];
int sz[maxn];
int fg = 1;
void dfs(int u, int now) {
  if (d[u] >= 3) {
    if (len[u][0] == now || len[u][1] == now)
      d[u]--;
    else if (len[u][0] == -1)
      len[u][0] = now, sz[u] = 1;
    else if (len[u][1] == -1)
      len[u][1] = now, sz[u] = 2;
    else
      fg = 0;
  } else
    len[u][0] = now, sz[u] = 1;
  if (d[u] >= 3) return;
  vis[u] = 1;
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (vis[v]) continue;
    dfs(v, now + 1);
  }
}
int main(int argc, char const *argv[]) {
  fg = 1;
  memset(len, -1, sizeof len);
  int n;
  scanf("%d", &n);
  int a, b;
  for (int i = 1; i < n; i++) {
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
    d[a]++;
    d[b]++;
  }
  int fp = 0;
  for (int i = 1; i <= n; i++) {
    if (d[i] == 1 && !vis[i]) dfs(i, 0), fp++;
  }
  int ans = 0, cnt = 0;
  for (int i = 1; i <= n; i++) {
    if (d[i] >= 3) cnt++;
    if (sz[i] == 2) ans = len[i][0] + len[i][1];
  }
  int q = n - 1;
  while (ans != 0 && ans % 2 == 0) ans /= 2;
  while (q != 0 && q % 2 == 0) q /= 2;
  if (fp == 1)
    printf("%d\n", q);
  else if (cnt >= 1 || !fg)
    printf("-1\n");
  else
    printf("%d\n", ans);
}
