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 = 2e5 + 10;
vector<int> g[N];
int dist[N], sol;
int n, r, c;
set<int> skup;
pair<int, int> dfs(int v, int prev, int d) {
  pair<int, int> ret = {d + 1, v};
  for (auto xt : g[v]) {
    if (xt == prev) continue;
    ret = max(ret, dfs(xt, v, d + 1));
  }
  return ret;
}
int center(int v, int prev, int d) {
  dist[v] = d + 1;
  for (auto xt : g[v]) {
    if (xt == prev) continue;
    center(xt, v, dist[v]);
  }
}
void finish() {
  printf("-1");
  exit(0);
}
void tr(int v, int prev, int d) {
  dist[v] = d + 1;
  for (auto xt : g[v]) {
    if (xt == prev) continue;
    if ((int)g[v].size() > 2) finish();
    tr(xt, v, dist[v]);
  }
  if ((int)g[v].size() == 1) skup.insert(dist[v]);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
  }
  pair<int, int> p = dfs(dfs(1, 0, -1).second, 0, -1);
  center(p.second, 0, -1);
  for (int i = 1; i <= n; i++)
    if (dist[i] == p.first / 2) c = i;
  for (auto xt : g[c]) tr(xt, c, 0);
  if ((int)skup.size() > 2) finish();
  for (auto len : skup) sol += len;
  printf("%d", (sol % 2 == 0) ? 1 : sol);
  return 0;
}
