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 T, N, M, L, tag[200005];
vector<int> node[200005];
void ini(void) {
  int i, j, k;
  scanf("%d", &N);
  for (i = 1; i < N; i++) {
    scanf("%d %d", &j, &k);
    node[j].push_back(k);
    node[k].push_back(j);
  }
}
int dfs(int x, int p, int first) {
  if (first) {
    int j, k = x;
    tag[x] = tag[p] + 1;
    for (int i = 0; i < node[x].size(); i++) {
      if (node[x][i] != p) {
        j = dfs(node[x][i], x, first);
        if (tag[j] > tag[k]) k = j;
      }
    }
    return k;
  } else {
    int j, k = 0;
    if (x != p && tag[x] - 1 <= tag[p] + 1 && tag[x] + 1 >= tag[p] + 1)
      return x;
    tag[x] = tag[p] + 1;
    for (int i = 0; i < node[x].size(); i++) {
      if (node[x][i] != p) {
        j = dfs(node[x][i], x, first);
        if (!k && j) k = j;
      }
    }
    return k;
  }
}
int combine(int x, int p) {
  int i, j, k = 0;
  map<int, int> ma;
  map<int, int>::iterator ite;
  for (i = 0; i < node[x].size(); i++) {
    if (node[x][i] != p) {
      j = combine(node[x][i], x);
      if (j < 0) return -1;
      ma[j]++;
    }
  }
  for (ite = ma.begin(), j = 0; ite != ma.end(); ++ite) {
    j++;
    k += ite->first;
  }
  if (x != p && j > 1) return -1;
  if (x == p && j > 2) return -1;
  return k + 1;
}
void sol(void) {
  int c = dfs(1, 1, 1);
  tag[c] = -1;
  c = dfs(c, c, 1);
  tag[c] = -1;
  c = dfs(c, c, 0);
  int ans = combine(c, c);
  if (ans < 0) {
    printf("-1\n");
  } else {
    --ans;
    while (!(ans & 1)) ans >>= 1;
    printf("%d\n", ans);
  }
}
int main(void) {
  int i, j;
  ini();
  sol();
}
