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 = 200010;
vector<int> g[N];
int h[N];
int n;
vector<int> ve;
bool line[N], deleted[N];
int dfs(int u, int last) {
  int ret = 0;
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == last or deleted[v]) continue;
    ret = max(ret, 1 + dfs(v, u));
  }
  return h[u] = ret;
}
vector<int> g2;
void dfs2(int u, int last) {
  g2.push_back(u);
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v != last and !deleted[v]) dfs2(v, u);
  }
}
int calc_deg(int u) {
  int ret = 0;
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (!deleted[v]) ret++;
  }
  return ret;
}
bool comp(int u, int v) { return h[u] < h[v]; }
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    g[u].push_back(v);
    g[v].push_back(u);
    ve.push_back(i + 1);
  }
  ve.push_back(n);
  dfs(1, -1);
  sort(ve.begin(), ve.end(), comp);
  for (int i = 0; i < ve.size(); i++) {
    int u = ve[i];
    set<int> s;
    int undeleted = 0;
    for (int j = 0; j < g[u].size(); j++) {
      int v = g[u][j];
      if (h[v] > h[u]) continue;
      if (line[v]) {
        if (s.count(h[v]))
          deleted[v] = true;
        else {
          s.insert(h[v]);
          undeleted++;
        }
      } else {
        undeleted++;
      }
    }
    if (undeleted < 2) line[u] = true;
  }
  dfs2(1, -1);
  int d1 = 0, d2 = 0, d3 = 0, vd3;
  for (int i = 0; i < g2.size(); i++) {
    int d = calc_deg(g2[i]);
    if (d == 1)
      d1++;
    else if (d == 2)
      d2++;
    else {
      d3++;
      vd3 = g2[i];
    }
  }
  if (d1 == 2 and d3 == 0) {
    int ans = g2.size() - 1;
    while (ans % 2 == 0) ans /= 2;
    printf("%d\n", ans);
    return 0;
  }
  if (d3 == 1) {
    dfs(vd3, -1);
    int undeleted = 0;
    set<int> s;
    for (int i = 0; i < g[vd3].size(); i++) {
      int v = g[vd3][i];
      if (deleted[v]) continue;
      if (!s.count(h[v])) {
        s.insert(h[v]);
        undeleted++;
      } else
        deleted[v] = true;
    }
    if (undeleted < 3) {
      g2.clear();
      dfs2(vd3, -1);
      int ans = g2.size() - 1;
      while (ans % 2 == 0) ans /= 2;
      printf("%d\n", ans);
      return 0;
    }
  }
  printf("-1\n");
  return 0;
}
