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 n;
set<int> A[200010];
void out(int x) {
  while (x % 2 == 0) x /= 2;
  printf("%d\n", x);
  exit(0);
}
map<int, vector<int> > B[200010];
set<pair<int, int> > C;
void add(int x, int y, int t) {
  B[x][t].push_back(y);
  if ((int)B[x][t].size() == 2) C.insert(make_pair(t, x));
}
int main() {
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int x, y;
    cin >> x >> y;
    x--;
    y--;
    A[x].insert(y);
    A[y].insert(x);
  }
  int now = n - 1;
  for (int i = 0; i < n; i++)
    if ((int)A[i].size() == 1) {
      int x = *A[i].begin(), y = i;
      int t = 1;
      while ((int)A[x].size() == 2) {
        int x1 = *A[x].begin();
        if (x1 == y) x1 = *A[x].rbegin();
        y = x;
        x = x1;
        t++;
      }
      if ((int)A[x].size() == 1) out(now);
      add(x, y, t);
    }
  while (!C.empty()) {
    pair<int, int> _x = *C.begin();
    C.erase(C.begin());
    int x = _x.second, t = _x.first;
    int m = (int)B[x][t].size();
    for (int i = 1; i < m; i++) {
      now -= t;
      A[x].erase(B[x][t][i]);
    }
    if ((int)A[x].size() == 1) out(now);
    if ((int)A[x].size() > 2) {
      B[x][t].resize(1);
      continue;
    }
    int y = B[x][t][0];
    B[x].erase(B[x].find(t));
    while ((int)A[x].size() == 2) {
      int x1 = *A[x].begin();
      if (x1 == y) x1 = *A[x].rbegin();
      y = x;
      x = x1;
      t++;
    }
    if ((int)A[x].size() == 1) out(now);
    add(x, y, t);
  }
  puts("-1");
  return 0;
}
