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 + 5;
vector<int> G[MAXN];
int dp[MAXN], len[MAXN];
void addEdge(int u, int v) {
  G[u].push_back(v);
  G[v].push_back(u);
}
int dfs(int u, int fa) {
  dp[u] = 1, len[u] = (int)G[u].size();
  bool vis[MAXN];
  memset(vis, 0, sizeof(vis));
  for (int i = 0; i < G[u].size(); i++) {
    int &v = G[u][i];
    if (v == fa) continue;
    int t = dfs(v, u);
    if (len[v] > 2)
      dp[u] += t;
    else {
      if (!vis[t]) {
        vis[t] = 1, dp[u] += t;
      } else {
        len[u]--, v = -1;
      }
    }
  }
  return dp[u];
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    addEdge(u, v);
  }
  int root;
  for (int i = 1; i <= n; i++)
    if (G[i].size() == 1) {
      root = i;
      break;
    }
  memset(dp, 0, sizeof(dp));
  dfs(root, -1);
  int node = 1;
  for (int i = 1; i <= n; i++)
    if (len[i] > len[node]) node = i;
  if (len[node] == 1)
    printf("%d\n", dp[root] - 1);
  else if (len[node] == 2) {
    if (dp[root] % 2)
      printf("%d\n", 1);
    else
      printf("%d\n", dp[root] - 1);
  } else if (len[node] <= 4) {
    bool flag = 1;
    for (int i = 1; i <= n; i++)
      if (i != node) {
        if (len[node] >= 3) {
          flag = 0;
          break;
        }
      }
    if (flag) {
      int a[10], k = 0, ans = 0;
      for (auto v : G[node]) {
        if (v == -1) continue;
        a[k++] = dp[v];
        ans += dp[v];
      }
      a[k++] = dp[root] - dp[node];
      ans += a[k - 1];
      sort(a, a + k);
      bool ok = 0;
      for (int i = k - 2; i >= 0; i--) {
        if (a[i] == a[i + 1]) {
          ans -= a[i];
          ok = 1;
          break;
        }
      }
      if (ok)
        printf("%d\n", ans);
      else
        puts("-1");
    } else
      puts("-1");
  } else
    puts("-1");
}
