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;
int n, m, x, y, t, mid, ans, k, head[N], dis1[N], dis2[N];
bool vis[N];
struct node {
  int too, Next;
} edge[N << 1];
inline void add(int a, int b) {
  edge[++t].too = b;
  edge[t].Next = head[a];
  head[a] = t;
}
inline void dfs(int u, int dep) {
  dis1[u] = dep;
  if (dep > ans) {
    ans = dep;
    k = u;
  }
  for (int i = head[u]; i; i = edge[i].Next) {
    int v = edge[i].too;
    if (!vis[v]) {
      vis[v] = true;
      dfs(v, dep + 1);
    }
  }
}
inline void dfs2(int u, int dep) {
  dis2[u] = dep;
  if (dep > ans) {
    ans = dep;
    k = u;
  }
  for (int i = head[u]; i; i = edge[i].Next) {
    int v = edge[i].too;
    if (!vis[v]) {
      vis[v] = true;
      dfs2(v, dep + 1);
    }
  }
}
inline int dp(int u, int fa) {
  set<int> s;
  set<int>::iterator it;
  for (int i = head[u]; i; i = edge[i].Next)
    if (edge[i].too != fa) s.insert(dp(edge[i].too, u));
  if (u == fa) {
    if (s.empty())
      return 0;
    else if (s.size() == 1)
      return *(s.begin()) + 1;
    else if (s.size() == 2) {
      return *(s.begin()) + *(--s.end()) + 2;
    } else {
      puts("-1");
      exit(0);
    }
  } else {
    if (s.empty())
      return 0;
    else if (s.size() == 1)
      return *(s.begin()) + 1;
    else {
      puts("-1");
      exit(0);
    }
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    scanf("%d%d", &x, &y);
    add(x, y);
    add(y, x);
  }
  vis[1] = true;
  dfs(1, 0);
  memset(vis, false, sizeof(vis));
  ans = 0;
  dfs(k, 0);
  cout << endl;
  memset(vis, false, sizeof(vis));
  ans = 0;
  dfs2(k, 0);
  for (int i = 1; i <= n; i++)
    if (dis1[i] + dis2[i] == ans &&
        min(dis1[i], dis2[i]) > min(dis1[mid], dis2[mid]))
      mid = i;
  ans = dp(mid, mid);
  while (ans % 2 == 0) ans >>= 1;
  printf("%d\n", ans);
  return 0;
}
