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;
vector<int> e[200010];
vector<bool> visited;
vector<bool> tvisited;
int ans = -1;
int dfs2(int x, int dis) {
  if (tvisited[x]) return -1;
  tvisited[x] = true;
  int tmp = -1;
  for (auto next : e[x]) {
    if (!tvisited[next]) {
      int ret = dfs2(next, dis + 1);
      if (ret < 0) return ret;
      if (tmp == -1) tmp = ret;
      if (tmp != ret) return -1;
    }
  }
  if (tmp == -1) {
    return dis;
  }
  return tmp;
}
void dfs3(int x, int dis) {
  if (tvisited[x]) return;
  tvisited[x] = true;
  int cnt = 0;
  for (auto next : e[x]) {
    if (!tvisited[next]) cnt++;
  }
  if (cnt == 1) {
    for (auto next : e[x]) {
      if (!tvisited[next]) dfs3(next, dis + 1);
    }
    return;
  }
  int tmp = -1;
  int fcnt = 0;
  int fi;
  visited = tvisited;
  for (auto next : e[x]) {
    if (!tvisited[next]) {
      int ret = dfs2(next, 0);
      if (ret < 0) {
        fcnt++;
        fi = next;
      } else if (ret != dis) {
        if (tmp == -1) tmp = ret;
        if (tmp != ret) return;
      }
    }
  }
  if (fcnt > 1) return;
  if (fcnt == 0) {
    ans = dis;
    if (tmp != -1) ans += tmp;
    return;
  }
  tvisited = visited;
  dfs3(fi, dis + 1);
}
void dfs(int x, int dis) {
  if (visited[x]) return;
  visited[x] = true;
  int cnt = 0;
  for (auto next : e[x]) {
    if (!visited[next]) {
      cnt++;
    }
  }
  if (cnt == 0) {
    ans = dis;
    return;
  }
  if (cnt == 1) {
    for (auto next : e[x]) {
      if (!visited[next]) {
        dfs(next, dis + 1);
      }
    }
    return;
  }
  int forkcnt = 0;
  int forki;
  set<int> s;
  s.insert(dis);
  tvisited = visited;
  for (auto next : e[x]) {
    if (!tvisited[next]) {
      int ret = dfs2(next, 1);
      if (ret >= 0)
        s.insert(ret);
      else {
        forkcnt++;
        forki = next;
      }
    }
  }
  if (s.size() > 2) return;
  if (forkcnt > 1) return;
  if (forkcnt == 1 && s.size() > 1) return;
  if (forkcnt == 0 && s.size() == 1) {
    ans = s.size();
    return;
  }
  if (forkcnt == 0 && s.size() == 2) {
    ans = 0;
    for (auto d : s) {
      ans += d;
    }
    return;
  }
  tvisited = visited;
  dfs3(forki, dis);
}
int main() {
  scanf("%d", &n);
  visited.resize(n);
  visited.resize(n);
  for (int i = 0; i < n - 1; i++) {
    int f, t;
    scanf("%d%d", &f, &t);
    f--;
    t--;
    e[f].push_back(t);
    e[t].push_back(f);
  }
  int leaf = -1;
  for (int i = 0; i < n; i++) {
    if (e[i].size() == 1) {
      leaf = i;
      break;
    }
  }
  assert(leaf != -1);
  dfs(leaf, 0);
  if (ans > 0) {
    while (ans % 2 == 0 && ans != 0) ans /= 2;
  }
  printf("%d\n", ans);
}
