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 long long INF = 1 << 28;
const long long LINF = 1ll << 61;
inline long long getnum() {
  register long long r = 0;
  register bool ng = 0;
  register char c;
  c = getchar();
  while (c != '-' && (c < '0' || c > '9')) c = getchar();
  if (c == '-') ng = 1, c = getchar();
  while (c >= '0' && c <= '9') r = r * 10 + c - '0', c = getchar();
  if (ng) r = -r;
  return r;
}
template <class T>
inline void putnum(T x) {
  if (x < 0) putchar('-'), x = -x;
  register short a[20] = {}, sz = 0;
  while (x > 0) a[sz++] = x % 10, x /= 10;
  if (sz == 0) putchar('0');
  for (int i = sz - 1; i >= 0; i--) putchar('0' + a[i]);
}
inline void putsp() { putchar(' '); }
inline void putendl() { putchar('\n'); }
inline char mygetchar() {
  register char c = getchar();
  while (c == ' ' || c == '\n') c = getchar();
  return c;
}
int n, tot = 1, head[800111], nxt[800111], to[800111], deg[800111];
int tv, mxlen, mxv, root;
void findf(int x, int pre = -1, int l = 1) {
  if (l > mxlen) {
    mxlen = l;
    mxv = x;
  }
  for (int i = head[x]; i; i = nxt[i]) {
    if (to[i] == pre) continue;
    findf(to[i], x, l + 1);
  }
}
void findr(int x, int pre = -1, int l = 1) {
  if (l == mxlen / 2 + 1) {
    root = x;
  }
  for (int i = head[x]; i; i = nxt[i]) {
    if (to[i] == pre) continue;
    findr(to[i], x, l + 1);
  }
}
set<int> st;
int dfs(int x, int pre = -1, int l = 0) {
  set<int> s;
  for (int i = head[x]; i; i = nxt[i]) {
    if (to[i] == pre) continue;
    int tmp = dfs(to[i], x, l + 1);
    s.insert(tmp);
  }
  if (deg[x] == 1) {
    st.insert(l);
    return l;
  }
  if (s.size() == 1)
    return *s.begin();
  else if (s.size() == 2 && x != root) {
    st.insert(23333333);
    st.insert(23333334);
    st.insert(23333335);
  }
}
void add(int x, int y) {
  nxt[++tot] = head[x];
  head[x] = tot;
  to[tot] = y;
  nxt[++tot] = head[y];
  head[y] = tot;
  to[tot] = x;
  deg[x]++;
  deg[y]++;
}
int main() {
  n = getnum();
  if (n == 2) {
    cout << 1 << endl;
    return 0;
  }
  for (int i = 1; i < n; i++) {
    int x, y;
    x = getnum(), y = getnum();
    add(x, n + i);
    add(n + i, y);
  }
  tv = 1;
  findf(tv);
  tv = mxv;
  mxlen = 0;
  findf(tv);
  findr(tv);
  dfs(root);
  if (st.size() > 2)
    puts("-1");
  else {
    int ans;
    if (st.size() == 2)
      ans = *st.begin() + *st.rbegin();
    else
      ans = *st.begin();
    while (ans % 2 == 0) ans /= 2;
    cout << ans << endl;
  }
  return 0;
}
