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;
vector<int> edge[200200];
int len[200200];
int flg;
void dfs(int u, int f, int d) {
  int son = -1;
  for (int i = 0; i < edge[u].size(); ++i) {
    if (edge[u][i] == f) continue;
    dfs(edge[u][i], u, d + 1);
    if (son != len[edge[u][i]]) {
      if (son == -1) {
        if (len[edge[u][i]] != d - 1) son = len[edge[u][i]];
      } else
        flg = 0;
    }
  }
  len[u] = son + 1;
}
int main() {
  int n, u, v;
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    scanf("%d %d", &u, &v);
    edge[u].push_back(v);
    edge[v].push_back(u);
  }
  int ans;
  flg = 1;
  for (int i = 1; i <= n; ++i) {
    if (edge[i].size() == 1) {
      dfs(i, -1, 0);
      if (flg) {
        ans = len[i];
        while ((ans & 1) == 0) ans /= 2;
      } else
        ans = -1;
      break;
    }
  }
  printf("%d\n", ans);
}
