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 Maxn = 2e5 + 10;
int n, m, h[Maxn], t, ans;
bool boo[Maxn], flag;
set<int> s[Maxn];
set<int>::iterator it;
struct GG {
  int node, Next;
} G[Maxn * 2];
void Insert(int a, int b) {
  m++;
  G[m].node = b;
  G[m].Next = h[a];
  h[a] = m;
}
int DFS(int p, int root) {
  s[p].clear();
  boo[p] = true;
  for (int Now = h[p]; Now != -1; Now = G[Now].Next)
    if (!boo[G[Now].node]) {
      int x = DFS(G[Now].node, root);
      if (!flag) return 0;
      it = s[p].find(x);
      if (it == s[p].end()) s[p].insert(x);
    }
  if (s[p].size() == 0) return 1;
  if (s[p].size() == 1) {
    it = s[p].begin();
    return (*it) + 1;
  }
  if (p == root && s[p].size() <= 2) {
    int sum = 0;
    for (it = s[p].begin(); it != s[p].end(); it++) sum += (*it);
    return sum + 1;
  }
  flag = false;
  t = p;
  return 0;
}
int main() {
  for (; scanf("%d", &n) != EOF;) {
    memset(h, -1, sizeof(h));
    m = -1;
    for (int i = 1; i < n; i++) {
      int x, y;
      scanf("%d%d", &x, &y);
      Insert(x, y), Insert(y, x);
    }
    memset(boo, 0, sizeof(boo));
    flag = true;
    ans = DFS(1, 1);
    if (!flag) {
      memset(boo, 0, sizeof(boo));
      flag = true;
      ans = DFS(t, t);
    }
    ans--;
    if (ans % 2 == 0) ans >>= 1;
    if (!flag)
      printf("-1\n");
    else
      printf("%d\n", ans);
  }
  return 0;
}
