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 main() {
  int n;
  cin >> n;
  vector<int> G[n];
  int x, y;
  for (int i = 0; i < n - 1; i++) {
    cin >> x >> y;
    G[x - 1].push_back(y - 1);
    G[y - 1].push_back(x - 1);
  }
  int P[n];
  for (int i = 0; i < n; i++) {
    if (G[i].size() == 1) {
      P[i] = 0;
    } else {
      P[i] = -1;
    }
  }
  int pr, pr1;
  while (1) {
    pr = 0;
    for (int i = 0; i < n; i++) {
      if ((G[i].size() == 1)) {
        y = G[i][0];
        if (G[y].size() == 2) {
          P[y] = P[i] + 1;
          P[i] = -1;
          G[i].clear();
          if (G[y][0] == i) {
            x = G[y][1];
          } else {
            x = G[y][0];
          }
          G[y].clear();
          G[y].push_back(x);
          pr = 1;
        } else {
          if (G[y].size() > 2) {
            pr1 = 0;
            for (int j = 0; j < (int)G[y].size(); j++) {
              if ((i != G[y][j]) && (P[G[y][j]] == P[i]) &&
                  (G[G[y][j]].size() == 1)) {
                pr1 = 1;
                break;
              }
            }
            if (pr1 == 1) {
              P[i] = -1;
              G[i].clear();
              vector<int> tmp;
              for (int j = 0; j < (int)G[y].size(); j++) {
                if (G[y][j] != i) {
                  tmp.push_back(G[y][j]);
                }
              }
              G[y] = tmp;
              pr = 1;
            }
          }
        }
      }
    }
    if (pr == 0) {
      break;
    }
  }
  int ans = 0, cnt = 0;
  for (int i = 0; i < n; i++) {
    if (P[i] != -1) {
      cnt++;
      ans += P[i];
    }
  }
  if (cnt != 2) {
    cout << -1 << endl;
  } else {
    cout << ans + 1 << endl;
  }
  return 0;
}
