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> G[200010];
int c[200010];
int bad[200100];
void dfs(int o, int fa) {
  bool tem = false;
  c[o] = -1;
  bad[o] = -1;
  for (auto &i : G[o]) {
    if (i == fa) continue;
    tem = true;
    dfs(i, o);
  }
  if (tem == false) {
    c[o] = 1;
    return;
  }
  for (auto &i : G[o]) {
    if (i == fa) continue;
    if (bad[i] != -1) {
      if (bad[o] != -1) {
        printf("-1\n");
        exit(0);
      }
      bad[o] = i;
    }
  }
  if (bad[o] != -1) return;
  int tmp = -1;
  for (auto &i : G[o]) {
    if (i == fa) continue;
    if (tmp == -1) {
      tmp = c[i];
      continue;
    }
    if (tmp != c[i]) {
      bad[o] = 0;
      return;
    }
  }
  c[o] = tmp + 1;
}
int ans;
void findB(int o) {
  if (bad[o] == 0) {
    vector<int> tt;
    for (auto &i : G[o]) {
      tt.push_back(c[i]);
    }
    sort(tt.begin(), tt.end());
    tt.resize(unique(tt.begin(), tt.end()) - tt.begin());
    if (tt.size() >= 3) {
      printf("-1\n");
      exit(0);
    }
    if (tt.size() == 1) {
      ans = tt[0];
    } else {
      ans = tt[0] + tt[1];
    }
    return;
  }
  int tmp = -1;
  for (auto &i : G[o]) {
    if (i == bad[o]) continue;
    if (tmp == -1) {
      tmp = c[i];
    }
    if (tmp != c[i]) {
      printf("-1\n");
      exit(0);
    }
  }
  if (tmp == -1) {
    c[o] = 1;
  } else {
    c[o] = tmp + 1;
  }
  findB(bad[o]);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  dfs(1, -1);
  if (c[1] > 0) {
    c[1]--;
    while (c[1] && c[1] % 2 == 0) c[1] /= 2;
    printf("%d\n", c[1]);
    return 0;
  }
  findB(1);
  while (ans % 2 == 0) ans /= 2;
  printf("%d\n", ans);
  return 0;
}
