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> graph[200010];
int check[200010];
bool check_path(int node, int parent) {
  if (graph[node].size() > 2) {
    return false;
  }
  bool ret = true;
  for (int i = 0; i < graph[node].size(); i++) {
    if (graph[node][i] == parent) {
      continue;
    }
    ret = check_path(graph[node][i], node);
  }
  return ret;
}
int get_len(int node, int parent) {
  if (graph[node].size() > 2) {
    if (check[node] > 5) {
      return -1;
    }
    vector<pair<int, int> > ve;
    vector<pair<int, int> > ve2;
    int p_len = -1;
    check[node]++;
    for (int i = 0; i < graph[node].size(); i++) {
      if (graph[node][i] == parent && !check_path(graph[node][i], node)) {
        continue;
      }
      int temp = get_len(graph[node][i], node);
      if (temp == -1) {
        return -1;
      }
      if (graph[node][i] == parent) {
        p_len = temp;
      }
      ve.push_back(pair<int, int>(temp, graph[node][i]));
    }
    sort(ve.begin(), ve.end());
    int cur = -1, ind = -1;
    for (int i = 0; i < ve.size(); i++) {
      if (ve[i].first != cur) {
        cur = ve[i].first;
        ind = ve[i].second;
        ve2.push_back(pair<int, int>(cur, ind));
      }
    }
    if (p_len == -1) {
      if (ve2.size() == 1) {
        return ve2[0].first + 1;
      }
      for (int i = 0; i < graph[node].size(); i++) {
        if (graph[node][i] == parent) {
          int temp = get_len(graph[node][i], node);
          if (temp == -1) {
            return -1;
          }
          p_len = temp;
          ve.push_back(pair<int, int>(temp, graph[node][i]));
        }
      }
      sort(ve.begin(), ve.end());
      ve2.clear();
      cur = -1, ind = -1;
      for (int i = 0; i < ve.size(); i++) {
        if (ve[i].first != cur) {
          cur = ve[i].first;
          ind = ve[i].second;
          ve2.push_back(pair<int, int>(cur, ind));
        }
      }
    }
    if (ve2.size() == 1) {
      return 1;
    } else if (ve2.size() == 2) {
      return ve2[0].first + ve2[1].first - p_len + 1;
    } else {
      return -1;
    }
  } else {
    int ret = 1;
    for (int i = 0; i < graph[node].size(); i++) {
      if (graph[node][i] != parent) {
        int temp = get_len(graph[node][i], node);
        if (temp == -1) {
          return -1;
        }
        ret += temp;
      }
    }
    return ret;
  }
}
int main(void) {
  scanf("%d", &N);
  for (int i = 1; i < N; i++) {
    int t1, t2;
    scanf("%d %d", &t1, &t2);
    graph[t1].push_back(t2);
    graph[t2].push_back(t1);
  }
  for (int i = 1; i <= N; i++) {
    sort(graph[i].begin(), graph[i].end());
  }
  int ans;
  for (int i = 1; i <= N; i++) {
    if (graph[i].size() == 1) {
      ans = get_len(i, 0);
      break;
    }
  }
  if (ans == -1) {
    printf("-1");
    return 0;
  }
  while (ans % 2 == 1) {
    ans = ans / 2 + 1;
  }
  printf("%d", ans - 1);
  return 0;
}
