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 dis[200010], dl[200010], dr[200010];
vector<int> vec[200010], vv[200010];
int read() {
  int s = 0, fh = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') fh = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    s = s * 10 + (ch - '0');
    ch = getchar();
  }
  return s * fh;
}
void dfs(int u, int fa) {
  int v;
  for (vector<int>::iterator it = vec[u].begin(); it != vec[u].end(); it++) {
    v = (*it);
    if (v == fa) continue;
    dis[v] = dis[u] + 1;
    dfs(v, u);
  }
}
void Solve(int u, int fa, int rt) {
  int v, val, i;
  bool yz = true;
  for (vector<int>::iterator it = vec[u].begin(); it != vec[u].end(); it++) {
    v = (*it);
    if (v == fa) continue;
    yz = false;
    Solve(v, u, rt);
    for (vector<int>::iterator it1 = vv[v].begin(); it1 != vv[v].end(); it1++) {
      val = (*it1);
      vv[u].push_back(val);
    }
  }
  sort(vv[u].begin(), vv[u].end());
  vv[u].resize(unique(vv[u].begin(), vv[u].end()) - vv[u].begin());
  if ((u == rt && (signed)vv[u].size() > 2) ||
      (u != rt && (signed)vv[u].size() > 1)) {
    printf("-1");
    exit(0);
  }
  if (u == rt) return;
  if (yz == true)
    vv[u].push_back(1);
  else {
    for (i = 0; i < (signed)vv[u].size(); i++) vv[u][i]++;
  }
}
int main() {
  int n, i, u, v, l, r, len, mx, mxi, rt, ans = 0;
  n = read();
  for (i = 1; i < n; i++) {
    u = read();
    v = read();
    vec[u].push_back(v);
    vec[v].push_back(u);
  }
  dis[1] = 0;
  dfs(1, 0);
  mx = 0;
  mxi = 0;
  for (i = 1; i <= n; i++)
    if (dis[i] > mx) {
      mx = dis[i];
      mxi = i;
    }
  l = mxi;
  dis[l] = 0;
  dfs(l, 0);
  for (i = 1; i <= n; i++) dl[i] = dis[i];
  mx = 0;
  mxi = 0;
  for (i = 1; i <= n; i++)
    if (dis[i] > mx) {
      mx = dis[i];
      mxi = i;
    }
  r = mxi;
  len = mx;
  dis[r] = 0;
  dfs(r, 0);
  for (i = 1; i <= n; i++) dr[i] = dis[i];
  rt = l;
  for (i = 1; i <= n; i++)
    if (dl[i] + dr[i] == len && min(dl[i], dr[i]) > min(dl[rt], dr[rt])) rt = i;
  Solve(rt, 0, rt);
  ans = 0;
  for (vector<int>::iterator it = vv[rt].begin(); it != vv[rt].end(); it++)
    ans += (*it);
  while (ans % 2 == 0) ans /= 2;
  printf("%d", ans);
  return 0;
}
