#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;
}
