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 N = 2e5 + 5;
vector<int> adj[N];
bool canMake[N];
set<int> s[N];
int d[N];
void dfs2(int &ret, int node, int p, int len) {
  if (canMake[node]) {
    set<int> tmp = s[node];
    tmp.insert(len);
    int R = 0;
    if (tmp.size() <= 2) {
      for (set<int>::iterator it = tmp.begin(); it != tmp.end(); ++it) {
        R += (*it);
      }
      while (R % 2 == 0) {
        R /= 2;
      }
      ret = min(ret, R);
    }
  }
  int makeCount = 0;
  map<int, int> dh;
  for (int i = 0; i < adj[node].size(); ++i) {
    int ch = adj[node][i];
    if (ch == p) {
      continue;
    }
    if (s[ch].size() >= 2 || !canMake[ch]) {
      ++makeCount;
    } else {
      ++dh[d[ch] + 1];
    }
  }
  if (len != 0) ++dh[len];
  for (int i = 0; i < adj[node].size(); ++i) {
    int ch = adj[node][i];
    if (ch == p) {
      continue;
    }
    if (s[ch].size() == 2 || !canMake[ch]) {
      --makeCount;
    } else {
      --dh[d[ch] + 1];
      if (dh[d[ch] + 1] == 0) {
        dh.erase(d[ch] + 1);
      }
    }
    if (makeCount == 0) {
      if (dh.size() == 1) {
        int tlen = (dh.begin())->first;
        dfs2(ret, ch, node, tlen + 1);
      } else if (dh.size() == 0) {
        int tlen = 1;
        dfs2(ret, ch, node, tlen);
      }
    }
    if (s[ch].size() == 2 || !canMake[ch]) {
      ++makeCount;
    } else {
      ++dh[d[ch] + 1];
    }
  }
}
void dfs(int node, int p) {
  canMake[node] = true;
  for (int i = 0; i < adj[node].size(); ++i) {
    int ch = adj[node][i];
    if (ch == p) {
      continue;
    }
    dfs(ch, node);
    if (!canMake[ch] || s[ch].size() > 1) {
      canMake[node] = false;
    } else {
      d[node] = d[ch] + 1;
      s[node].insert(d[node]);
      if (s[node].size() > 2) {
        canMake[node] = false;
      }
    }
  }
  if (s[node].size() > 2) {
    canMake[node] = false;
  }
}
void solve() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n - 1; ++i) {
    int a, b;
    scanf("%d %d", &a, &b);
    adj[a].push_back(b);
    adj[b].push_back(a);
  }
  dfs(1, 0);
  int ret = 1e9;
  dfs2(ret, 1, 0, 0);
  if (ret == 1e9) {
    ret = -1;
  }
  printf("%d\n", ret);
}
int main() { solve(); }
