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 = 200005;
vector<int> maps[N], Q;
int num[N];
int ans[N], root;
bool flag;
void dfs(int u, int fa) {
  int pre = -1, length = 0, cnt = 0;
  for (int i = 0; i < (int)maps[u].size(); i++) {
    int v = maps[u][i];
    if (v == fa) continue;
    cnt++;
    dfs(v, u);
    if (ans[v] != pre && cnt != 1 && u != root) {
      flag = false;
    }
    length = ans[v];
    pre = ans[v];
  }
  ans[u] = length + 1;
}
int main() {
  int n;
  scanf("%d", &n);
  int maxx = 0;
  for (int i = 2; i <= n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    maps[u].push_back(v);
    maps[v].push_back(u);
    num[u]++, num[v]++;
    if (num[u] > maxx) {
      maxx = num[u];
      root = u;
    }
    if (num[v] > maxx) {
      maxx = num[v];
      root = v;
    }
  }
  flag = true;
  dfs(root, -1);
  for (int i = 0; i < (int)maps[root].size(); i++) {
    Q.push_back(ans[maps[root][i]]);
  }
  sort(Q.begin(), Q.end());
  int cnt = 1;
  for (int i = 0; i < (int)Q.size(); i++) {
    if (i && Q[i] != Q[i - 1]) cnt++;
  }
  int answer = 0;
  if (Q[0] == Q[Q.size() - 1])
    answer = Q[0];
  else {
    answer = Q[0] + Q[Q.size() - 1];
  }
  if (cnt > 2) flag = false;
  if (!flag)
    cout << "-1" << endl;
  else {
    while (answer % 2 == 0) {
      answer /= 2;
    }
    printf("%d\n", answer);
  }
}
