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;
vector<int> adj[500105];
int len[500105], junta[500105], ans = 1000000000;
void dfs(int x, int pai, int lenUp) {
  map<int, int> mapa;
  if (lenUp != 0) mapa[lenUp]++;
  int cnt = 0, idx;
  for (int i = 0, y; i < ((int)(adj[x]).size()); i++) {
    y = adj[x][i];
    if (y == pai) continue;
    mapa[len[y]]++;
    if (!junta[y]) {
      cnt++;
      idx = y;
    }
  }
  if (cnt > 1) return;
  if (((int)(mapa).size()) > 2) return;
  if (((int)(mapa).size()) == 1 && cnt == 0) {
    ans = min(ans, mapa.begin()->first);
  } else if (((int)(mapa).size()) == 2 && cnt == 0) {
    ans = min(ans, mapa.begin()->first + ((++mapa.begin())->first));
  }
  if (cnt == 1) {
    int a, b;
    a = mapa.begin()->first;
    if (((int)(mapa).size()) == 1) {
      if (mapa[a] == 1)
        dfs(idx, x, lenUp + 1);
      else
        dfs(idx, x, a + 1);
    } else {
      b = (++mapa.begin())->first;
      if (len[idx] != a) swap(a, b);
      if (mapa[a] == 1) dfs(idx, x, b + 1);
    }
  } else {
    int a, b;
    a = mapa.begin()->first;
    for (int i = 0, y; i < ((int)(adj[x]).size()); i++) {
      y = adj[x][i];
      if (y == pai) continue;
      if (((int)(mapa).size()) == 1) {
        if (mapa[a] == 1)
          dfs(y, x, lenUp + 1);
        else
          dfs(y, x, a + 1);
      } else {
        b = (++mapa.begin())->first;
        if (len[y] != a) swap(a, b);
        if (mapa[a] == 1) dfs(y, x, b + 1);
      }
    }
  }
}
void init(int x, int pai) {
  junta[x] = 1;
  if (((int)(adj[x]).size()) == 1 && x != pai) len[x] = 1;
  for (int i = 0, y; i < ((int)(adj[x]).size()); i++) {
    y = adj[x][i];
    if (y == pai) continue;
    init(y, x);
    if (len[x] != -1 && len[y] + 1 != len[x]) junta[x] = 0;
    len[x] = max(len[x], len[y] + 1);
    if (!junta[y]) junta[x] = 0;
  }
}
int main() {
  int n;
  cin >> n;
  for (int i = 1, x, y; i < n; i++) {
    cin >> x >> y;
    x--;
    y--;
    adj[x].push_back(y);
    adj[y].push_back(x);
  }
  memset(len, -1, sizeof(len));
  init(0, 0);
  dfs(0, 0, 0);
  while (ans % 2 == 0) {
    ans /= 2;
  }
  if (ans == 1000000000)
    cout << -1 << endl;
  else
    cout << ans << endl;
}
