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> g[200005];
queue<pair<int, int> > q;
int deg[200005], a, n;
bool v[200005];
set<int> s[200005];
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
    deg[a]++, deg[b]++;
  }
  for (int i = 1; i <= n; i++)
    if (deg[i] == 1) q.push(pair<int, int>(i, 0));
  int c = 0, lst = -1;
  while (!q.empty()) {
    int x = q.front().first, d = q.front().second;
    q.pop();
    v[x] = true;
    lst = x, c++;
    for (auto y : g[x]) {
      if (v[y]) continue;
      deg[y]--;
      s[y].insert(d + 1);
      if (deg[y] == 1 and s[y].size() == 1) q.push(pair<int, int>(y, d + 1));
    }
  }
  if (c < n - 1)
    a = -1;
  else {
    if (c == n - 1)
      for (int i = 1; i <= n; i++)
        if (!v[i]) lst = i;
    if (s[lst].size() > 2)
      a = -1;
    else {
      for (auto e : s[lst]) a += e;
    }
  }
  while (a % 2 == 0) a /= 2;
  printf("%d\n", a);
}
