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>
int n, root;
std::vector<int> vec[(200010)];
int dis1[(200010)], dis2[(200010)], len[(200010)], ans;
void bfs(int u, int *dis) {
  memset(dis, -1, sizeof(int) * (200010));
  dis[u] = 0;
  std::queue<int> queue;
  queue.push(u);
  while (!queue.empty()) {
    u = queue.front();
    queue.pop();
    for (auto v : vec[u]) {
      if (dis[v] == -1) {
        dis[v] = dis[u] + 1;
        queue.push(v);
      }
    }
  }
}
bool dfs(int u, int fa) {
  if (u == root) {
    std::set<int> set;
    for (auto v : vec[u]) {
      if (v == fa) continue;
      if (!dfs(v, u)) return false;
      set.insert(len[v]);
    }
    if ((int)(set.size()) > 2) return false;
    for (auto v : set) {
      ans += v + 1;
    }
    return true;
  }
  int now = -1;
  for (auto v : vec[u]) {
    if (v == fa) continue;
    if (!dfs(v, u)) return false;
    if (now == -1) {
      now = len[v];
    } else if (now != len[v]) {
      return false;
    }
  }
  len[u] = now + 1;
  return true;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    vec[u].push_back(v);
    vec[v].push_back(u);
  }
  bfs(1, dis1);
  int u = 0, v = 0;
  for (int i = 1; i <= n; ++i) {
    if (dis1[i] > dis1[u]) {
      u = i;
    }
  }
  bfs(u, dis1);
  for (int i = 1; i <= n; ++i) {
    if (dis1[i] > dis1[v]) {
      v = i;
    }
  }
  bfs(v, dis2);
  for (int i = 1; i <= n; ++i) {
    if (dis1[i] + dis2[i] == dis1[v] && std::abs(dis1[i] - dis2[i]) <= 1) {
      root = i;
      break;
    }
  }
  if (!dfs(root, 0)) {
    printf("-1\n");
  } else {
    while (!(ans % 2)) ans >>= 1;
    printf("%d\n", ans);
  }
  return 0;
}
