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 lnk[200005], nxt[200005 * 2], son[200005 * 2], tot;
void add(int x, int y) {
  nxt[++tot] = lnk[x];
  lnk[x] = tot;
  son[tot] = y;
}
inline int min(int x, int y) { return x < y ? x : y; }
inline long long min(long long x, long long y) { return x < y ? x : y; }
inline double min(double x, double y) { return x < y ? x : y; }
inline int max(int x, int y) { return x > y ? x : y; }
inline long long max(long long x, long long y) { return x > y ? x : y; }
inline double max(double x, double y) { return x > y ? x : y; }
inline void swap(int& x, int& y) {
  int t = x;
  x = y;
  y = t;
}
inline void swap(long long& x, long long& y) {
  long long t = x;
  x = y;
  y = t;
}
inline void swap(double& x, double& y) {
  double t = x;
  x = y;
  y = t;
}
int outarr[30];
template <class T>
inline void pt(T x) {
  if (x < 0) putchar('-'), x = -x;
  outarr[0] = 0;
  do {
    outarr[++outarr[0]] = x % 10;
    x /= 10;
  } while (x);
  for (int i = outarr[0]; i; i--) putchar(outarr[i] + '0');
}
template <class T>
inline void rd(T& x) {
  x = 0;
  int c = getchar(), f = 0;
  while ((c < '0' || c > '9') && c != '-') c = getchar();
  if (c == '-') f = 1, c = getchar();
  while (c >= '0' && c <= '9') x = (x << 1) + (x << 3) + c - '0', c = getchar();
  f ? x = -x : 0;
}
inline int rint() {
  int c = getchar(), f = 0, x = 0;
  while ((c < '0' || c > '9') && c != '-') c = getchar();
  if (c == '-') f = 1, c = getchar();
  while (c >= '0' && c <= '9') x = (x << 1) + (x << 3) + c - '0', c = getchar();
  return f ? -x : x;
}
inline long long rll() {
  int c = getchar(), f = 0;
  long long x = 0;
  while ((c < '0' || c > '9') && c != '-') c = getchar();
  if (c == '-') f = 1, c = getchar();
  while (c >= '0' && c <= '9') x = (x << 1) + (x << 3) + c - '0', c = getchar();
  return f ? -x : x;
}
int q = -1, n;
int check(int x, int fa) {
  int p = -1;
  for (int i = lnk[x]; i; i = nxt[i])
    if (fa != son[i]) {
      int y = check(son[i], x);
      if (p == -1)
        p = y;
      else if (p != y)
        if (fa != 0) {
          printf("-1\n");
          exit(0);
        } else if (q == -1)
          q = y;
        else if (q != y) {
          printf("-1\n");
          exit(0);
        }
    }
  if (!fa) {
    int ans = p + q + 2;
    while ((ans > 0) && (!(ans & 1))) ans /= 2;
    printf("%d\n", ans);
    exit(0);
  }
  return p + 1;
}
int dfs(int x, int fa) {
  int p = -1;
  for (int i = lnk[x]; i; i = nxt[i])
    if (fa != son[i]) {
      int y = dfs(son[i], x);
      if (p == -1)
        p = y;
      else if (p != y)
        check(x, 0);
    }
  if (!fa) check(x, 0);
  return p + 1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int x, y;
    rd(x);
    rd(y);
    add(x, y);
    add(y, x);
  }
  int ans = dfs(1, 0);
  printf("%d\n", (ans & 1) ? (ans / 2) : 0);
}
