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 MAX = 200200;
int head[MAX], nxt[MAX * 2], to[MAX * 2], dpthMx[MAX], dpthMn[MAX], Ecnt, n;
int ch[MAX], sz;
void dfs(int cur, int par) {
  for (int i = head[cur]; ~i; i = nxt[i])
    if (to[i] != par) {
      dfs(to[i], cur);
      dpthMn[cur] = min(dpthMn[cur], dpthMn[to[i]] + 1);
      dpthMx[cur] = max(dpthMx[cur], dpthMx[to[i]] + 1);
    }
  if (dpthMn[cur] == MAX) dpthMn[cur] = 0;
}
int getNxt(int cur) {
  int mx3[3]{}, mn3[3]{};
  for (int i = head[cur]; ~i; i = nxt[i]) {
    mn3[0] = mx3[0] = to[i];
    sort(mn3, mn3 + 3, [](int a, int b) { return dpthMn[a] > dpthMn[b]; });
    sort(mx3, mx3 + 3, [](int a, int b) { return dpthMx[a] < dpthMx[b]; });
  }
  if (dpthMx[mx3[2]] - dpthMx[mx3[1]] < 2) return 0;
  dpthMx[cur] = dpthMx[mx3[1]] + 1;
  dpthMn[cur] = mn3[2] != mx3[2] ? (dpthMn[mn3[2]] + 1)
                : mn3[1]         ? (dpthMn[mn3[1]] + 1)
                                 : 0;
  return mx3[2];
}
void addEdge(int u, int v) {
  nxt[Ecnt] = head[u];
  head[u] = Ecnt;
  to[Ecnt++] = v;
}
int main() {
  scanf("%d", &n);
  memset(head, -1, (n + 1) * sizeof head[0]);
  dpthMx[0] = -1;
  dpthMn[0] = MAX;
  fill(dpthMn, dpthMn + n + 1, MAX);
  for (int i = 1, u, v; i < n; ++i) {
    scanf("%d%d", &u, &v);
    addEdge(u, v);
    addEdge(v, u);
  }
  dfs(1, 0);
  int cen = 1, ncen;
  while (ncen = getNxt(cen)) cen = ncen;
  dpthMx[0] = 0;
  for (int i = head[cen]; ~i; i = nxt[i]) {
    if (dpthMx[to[i]] != dpthMn[to[i]]) return puts("-1"), 0;
    ch[sz++] = dpthMx[to[i]] + 1;
  }
  sort(ch, ch + sz);
  sz = unique(ch, ch + sz) - ch;
  if (sz > 2) return puts("-1"), 0;
  ch[sz] = 0;
  int ans = ch[0] + ch[1];
  while (!(ans & 1)) ans >>= 1;
  printf("%d\n", ans);
  return 0;
}
