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;
const int INF = 0x3f3f3f3f;
struct node {
  int v, next;
} pos[4 * maxn];
int n, cnt, tosize, toans, toflag;
int size[maxn], head[maxn], vis[maxn];
void init() {
  cnt = 1;
  tosize = INF;
  toans = INF;
  toflag = 0;
  memset(size, 0, sizeof(size));
  memset(head, -1, sizeof(head));
  memset(vis, 0, sizeof(vis));
}
void add(int a, int b, int c) {
  pos[cnt].v = b;
  pos[cnt].next = head[a];
  head[a] = cnt++;
}
void dfs(int x) {
  int sum = 0;
  int y;
  vis[x] = 1;
  for (int i = head[x]; i != -1; i = pos[i].next) {
    y = pos[i].v;
    if (vis[y] == 1 || y == x) continue;
    dfs(y);
    size[x] += size[y] + 1;
    sum = max(sum, size[y] + 1);
  }
  sum = max(sum, n - (size[x] + 1));
  if (sum < tosize || (sum == tosize && x < toans)) {
    toans = x;
    tosize = sum;
  }
}
void dfs1(int x) {
  int y;
  int pos1 = 0;
  int pos2[5], tot = 0;
  memset(pos2, 0, sizeof(pos2));
  vis[x] = 1;
  size[x]++;
  for (int i = head[x]; i != -1; i = pos[i].next) {
    y = pos[i].v;
    if (vis[y] == 1 || y == x) continue;
    dfs1(y);
    if (x == toans) {
      if (tot == 1) {
        if (pos2[0] != size[y]) pos2[tot++] = size[y];
      } else if (tot == 0) {
        pos2[tot++] = size[y];
      } else {
        if (size[y] != pos2[0] && size[y] != pos2[1]) toflag = 1;
      }
    } else {
      if (!pos1) {
        pos1 = size[y];
      } else {
        if (size[y] != pos1) toflag = 1;
      }
    }
  }
  if (!toflag) {
    if (x != toans)
      size[x] += pos1;
    else {
      for (int i = 0; i < tot; i++) size[x] += pos2[i];
    }
  }
}
int main() {
  int a, b;
  init();
  cin >> n;
  for (int i = 1; i < n; i++) {
    cin >> a >> b;
    add(a, b, 0);
    add(b, a, 0);
  }
  dfs(1);
  memset(size, 0, sizeof(size));
  memset(vis, 0, sizeof(vis));
  dfs1(toans);
  if (toflag == 1)
    cout << -1 << endl;
  else {
    if (size[toans] % 2 != 0) {
      for (;;) {
        size[toans] = (size[toans] + 1) / 2;
        if (size[toans] % 2 == 0) break;
      }
    }
    cout << size[toans] - 1 << endl;
  }
  return 0;
}
