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;
static struct { int v, next; } edge[2 * 200010];
static int N, G, ids, ans, head[200010], deg[200010], vis[200010];
static queue<int> Q;
static vector<int> len[200010];
inline void add_edge(int u, int v) {
  deg[u]++;
  deg[v]++;
  edge[G].v = v;
  edge[G].next = head[u];
  head[u] = G++;
  edge[G].v = u;
  edge[G].next = head[v];
  head[v] = G++;
}
int main() {
  memset(head, -1, sizeof(head));
  scanf("%d", &N);
  for (int i = 1, u, v; i < N; i++) scanf("%d%d", &u, &v), add_edge(u, v);
  for (int i = 1; i <= N; i++)
    if (deg[i] == 1) Q.push(i), len[i].push_back(0);
  while (!Q.empty()) {
    int x = Q.front();
    Q.pop();
    sort(len[x].begin(), len[x].end());
    len[x].resize(unique(len[x].begin(), len[x].end()) - len[x].begin());
    if (len[x].size() > 1)
      if (ids)
        return printf("-1\n"), 0;
      else {
        ids = x;
        continue;
      }
    vis[x] = 1;
    ans = len[x][0];
    for (int i = head[x]; ~i; i = edge[i].next)
      if (!vis[edge[i].v]) {
        len[edge[i].v].push_back(len[x][0] + 1);
        if (--deg[edge[i].v] == 1) Q.push(edge[i].v);
      }
  }
  if (ids) {
    sort(len[ids].begin(), len[ids].end());
    len[ids].resize(unique(len[ids].begin(), len[ids].end()) -
                    len[ids].begin());
    if (len[ids].size() > 2) return printf("-1\n"), 0;
    ans = len[ids][0] + (len[ids].size() == 2 ? len[ids][1] : 0);
  }
  while (ans % 2 == 0) ans /= 2;
  printf("%d\n", ans);
  return 0;
}
