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;
vector<int> V[200010], V2[200010];
int n, l, koren, x, br, s, br2;
int o[200010], c[200010], brc[2000010];
int dfs(int i) {
  o[i] = 1;
  if ((V[i].size() == 1) && (o[V[i][0]])) return 1;
  for (int j = 0; j < V[i].size(); j++) {
    if (!o[V[i][j]])
      V2[i].push_back(dfs(V[i][j])), brc[i] += V2[i][V2[i].size() - 1];
    if (x == 2) return -1;
  }
  sort(V2[i].begin(), V2[i].end());
  if (x == 1) {
    if (V2[i].size() > 1) {
      x = 2;
      return -1;
    }
  } else {
    br = 1;
    for (int j = 1; j < V2[i].size(); j++)
      if (V2[i][j] != V2[i][j - 1])
        br++;
      else
        brc[i] -= V2[i][j];
    if (br > 1) {
      x = 1;
      koren = i;
      c[1] = V2[i][0];
      l = 1;
      for (int j = 1; j < V2[i].size(); j++)
        if (V2[i][j] != V2[i][j - 1]) c[++l] = V2[i][j];
      l = br;
    }
    return brc[i];
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) o[i] = 0, brc[i] = 1;
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    V[x].push_back(y);
    V[y].push_back(x);
  }
  o[1] = 1;
  koren = 0;
  s = 0;
  for (int i = 0; i < V[1].size(); i++) {
    x = 0;
    br2 = dfs(V[1][i]);
    s += x;
    if ((br2 == -1) || (s > 1)) {
      printf("-1");
      return 0;
    }
    if (!x) V2[1].push_back(br2);
    brc[1] += br2;
  }
  sort(V2[1].begin(), V2[1].end());
  br = 1;
  for (int i = 1; i < V2[1].size(); i++)
    if (V2[1][i] != V2[1][i - 1]) br++;
  if (koren) {
    if ((br >= 2) || (l > 2)) {
      printf("-1");
      return 0;
    }
    x = brc[1] - brc[x];
    for (int i = 1; i <= l; i++)
      if (x == c[i]) {
        br = -1;
        break;
      }
    if (br == -1) {
      printf("-1");
      return 0;
    }
    printf("%d", brc[koren] - 1);
  } else {
    if (br > 2) {
      printf("-1");
      return 0;
    }
    if (br <= 2) {
      if (brc[1] % 2 == 1)
        printf("%d", brc[1] / 2);
      else if (br == 1)
        printf("%d", V2[1][0]);
    } else
      printf("%d", brc[1] - 1);
  }
  return 0;
}
