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 n, head[200005], cnt, d[200005], dis1[200005], dis2[200005];
struct node {
  int v, nx;
} e[400005];
inline int read() {
  int ret = 0, ff = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') ff = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    ret = (ret << 3) + (ret << 1) + (ch ^ 48);
    ch = getchar();
  }
  return ret * ff;
}
void add(int x, int y) {
  e[++cnt].v = y;
  e[cnt].nx = head[x];
  head[x] = cnt;
}
void dfs(int now, int fa) {
  d[now] = d[fa] + 1;
  for (int i = head[now]; i; i = e[i].nx) {
    int v = e[i].v;
    if (v != fa) dfs(v, now);
  }
}
void dfs1(int now, int fa) {
  for (int i = head[now]; i; i = e[i].nx) {
    int v = e[i].v;
    if (v != fa) {
      dis1[v] = dis1[now] + 1;
      dfs1(v, now);
    }
  }
}
void dfs2(int now, int fa) {
  for (int i = head[now]; i; i = e[i].nx) {
    int v = e[i].v;
    if (v != fa) {
      dis2[v] = dis2[now] + 1;
      dfs2(v, now);
    }
  }
}
int solve(int now, int fa) {
  set<int> s;
  for (int i = head[now]; i; i = e[i].nx) {
    int v = e[i].v;
    if (v != fa) s.insert(solve(v, now));
  }
  if (now == fa) {
    if (s.empty()) return 0;
    if (s.size() == 1) return *(s.begin()) + 1;
    if (s.size() == 2) return *(s.begin()) + *(--s.end()) + 2;
    if (s.size() > 2) {
      printf("-1");
      exit(0);
    }
  } else {
    if (s.empty()) return 0;
    if (s.size() == 1) return *(s.begin()) + 1;
    if (s.size() > 1) {
      printf("-1");
      exit(0);
    }
  }
}
int main() {
  n = read();
  for (int i = 1; i < n; i++) {
    int x = read(), y = read();
    add(x, y);
    add(y, x);
  }
  dfs(1, 0);
  int maxd = 0, maxd_id;
  for (int i = 1; i <= n; i++)
    if (d[i] > maxd) maxd = d[i], maxd_id = i;
  dfs1(maxd_id, 0);
  int far = 0, maxf_id;
  for (int i = 1; i <= n; i++)
    if (dis1[i] > far) far = dis1[i], maxf_id = i;
  dfs2(maxf_id, 0);
  int mid = 0;
  for (int i = 1; i <= n; i++) {
    if (dis1[i] + dis2[i] == far) {
      if (!mid)
        mid = i;
      else if (min(dis1[i], dis2[i]) > min(dis1[mid], dis2[mid]))
        mid = i;
    }
  }
  int ans = solve(mid, mid);
  while (ans % 2 == 0) ans >>= 1;
  printf("%d", ans);
  return 0;
}
