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> a[300000];
vector<int> b[300000];
vector<int> t;
int p[300000];
bool k[300000];
int n;
int m;
int u, v;
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    scanf("%d %d", &u, &v);
    u--;
    v--;
    a[u].push_back(v);
    a[v].push_back(u);
  }
  for (int i = 0; i < n; i++) {
    p[i] = a[i].size();
    k[i] = false;
  }
  m = n;
  for (int i = 0; i < n; i++)
    if (p[i] == 1) t.push_back(i);
  int ind = 0;
  int x;
  while (ind < t.size()) {
    u = t[ind];
    k[u] = true;
    v = -1;
    for (int i = 0; i < a[u].size(); i++)
      if (!k[a[u][i]]) v = a[u][i];
    if (v != -1) {
      x = 0;
      p[v]--;
      if (p[v] == 1) t.push_back(v);
      if (b[u].size() > 0) {
        x = b[u][0];
        for (int i = 1; i < b[u].size(); i++) {
          if (b[u][i] != x) {
            printf("-1");
            return 0;
          }
        }
      }
      b[v].push_back(x + 1);
    }
    ind++;
  }
  for (int i = 0; i < n; i++)
    if (!k[i]) u = i;
  if (b[u].size() == 1)
    x = b[u][0];
  else {
    sort(b[u].begin(), b[u].end());
    x = b[u][0];
    for (int i = 1; i < b[u].size(); i++) {
      if (b[u][i] != b[u][i - 1]) {
        x += b[u][i];
      }
    }
  }
  while (x % 2 == 0) x = x / 2;
  printf("%d", x);
  return 0;
}
