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 maxn = 200001;
int n, togo[maxn], tlen, par[maxn], cq[maxn];
unordered_map<int, int> len[maxn];
vector<int> edge[maxn];
int out(int i) {
  while (!(i & 1)) i >>= 1;
  cout << i << '\n';
  return 0;
}
void dfs(int now, int last = 0) {
  par[now] = last;
  cq[now] = edge[now].size();
  for (int &k : edge[now])
    if (k != last) dfs(k, now);
  --cq[now];
}
void dfs2(int now, int last = 0) {
  par[now] = last;
  cq[now] = 0;
  for (int &k : edge[now])
    if (k != last) dfs2(k, now), ++cq[now];
  if (cq[now] == 0) togo[tlen++] = now, len[now][0] = 1;
}
int rootit(int root) {
  tlen = 0;
  for (int i = 1; i <= n; ++i) len[i].clear();
  dfs2(root);
  for (int i = 0, now; i < n; ++i) {
    now = togo[i];
    if (len[now].size() == 2) {
      if (i == n - 1) {
        int res = 0;
        for (auto &j : len[now]) res += j.first;
        return out(res);
      } else {
        cout << -1;
        return 0;
      }
    }
    if (len[now].size() > 2) {
      cout << -1;
      return 0;
    }
    ++len[par[now]][len[now].begin()->first + 1];
    if (--cq[par[now]] == 0) togo[tlen++] = par[now];
  }
  return out(len[togo[n - 1]].begin()->first);
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> n;
  for (int a, b, i = 1; i < n; ++i) {
    cin >> a >> b;
    edge[a].push_back(b);
    edge[b].push_back(a);
  }
  for (int i = 1; i <= n; ++i)
    if (edge[i].size() == 1)
      togo[tlen++] = i, len[i][0] = 1;
    else if (tlen + 1 == i)
      dfs(i);
  if (tlen == 2) {
    out(n - 1);
  } else {
    for (int i = 0, now; i < n; ++i) {
      now = togo[i];
      if (len[now].size() == 2) {
        if (i == n - 1) {
          int res = 0;
          for (auto &j : len[now]) res += j.first;
          return out(res);
        } else {
          return rootit(now);
        }
      }
      if (len[now].size() > 2) {
        return rootit(now);
      }
      ++len[par[now]][len[now].begin()->first + 1];
      if (--cq[par[now]] == 0) togo[tlen++] = par[now];
    }
    out(len[togo[n - 1]].begin()->first);
  }
}
