#include <bits/stdc++.h>
using namespace std;

const int N = 4141;

int n;
vector<int> g[N];
bool cut_point[N];
int color[N], hsh[N], cnt[N];
vector<vector<int>> trees[N];

int dfs(int u, int p) {
  int ans = 1;
  vector<int> sz;
  for (int v : g[u]) {
    if (v != p) {
      int z = dfs(v, u);
      ans += z;
      sz.push_back(z);
    }
  }
  sz.push_back(n - ans);
  bool ok = true;
  for (int x : sz)
    ok &= (x == sz[0]);
  cut_point[u] = ok && sz.size() > 1;
  return ans;
}

void dfs2(int u, int p, int c) {
  color[u] = c;
  for (int v : g[u])
    if (v != p)
      dfs2(v, u, c);
}

void dfs3(int u, int p) {
  int c = color[u];
  hsh[u] = cnt[c];
  ++cnt[c];
  for (int v : g[u]) {
    if (v != p) {
      dfs3(v, u);
      trees[c][hsh[u]].push_back(hsh[v]);
      trees[c][hsh[v]].push_back(hsh[u]);
    }
  }
}

bool isomorphic(int t1, int t2) {
  // cek if trees[t1].isomorphling(trees[t2]);
}

int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; ++i) {
    int u, v;
    scanf("%d %d", &u, &v);
    --u, --v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs(0, -1);
  int cnt = 0;
  for (int i = 0; i < n; ++i)
    cnt += cut_point[i];
  if (!cnt)
    return 0 * puts("-1");
  assert(cnt == 1);
  int root;
  for (int i = 0; i < n; ++i)
    if (cut_point[i])
      root = i;
  int p = 0;
  for (int v : g[root]) {
    color[v] = ++p;
    dfs2(v, root, p);
  }
  int sz = 0;
  for (int i = 0; i < n; ++i)
    if (color[i] == 1)
      ++sz;
  for (int i = 1; i <= p; ++i)
    trees[i].resize(sz);
  for (int v : g[root])
    dfs3(v, root);
  // bool ok = true;
  // for (int i = 1; i < p; ++i)
  //   ok &= isomorphic(i, i + 1);
  // printf("%d\n", (ok ? p : -1));
  return 0;
}