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 N;
int x, y, root = -1;
vector<int> g[200100];
int len[200100], par[200100], viz[200100];
int ok, rootkids, magic, magic2;
void dfs(int x, int p) {
  par[x] = p;
  viz[x] = 1;
  if (g[x].size() == 1) {
    len[x] = 1;
  } else {
    int okk = 1;
    int kiddo = -1, kiddo2 = -1;
    for (auto y : g[x]) {
      if (viz[y]) {
        continue;
      }
      dfs(y, x);
      if (x == root) {
        if (len[y] == 0) {
          okk = 0;
          magic = y;
          ++rootkids;
        } else if (kiddo == -1) {
          magic2 = y;
          ++rootkids;
          kiddo = len[y];
        } else if (kiddo != len[y] && kiddo2 == -1) {
          ++rootkids;
          kiddo2 = len[y];
        } else if (kiddo2 != len[y] && kiddo != len[y]) {
          okk = 0;
          ++rootkids;
        }
      } else {
        if (len[y] == 0) {
          ok = 0;
          continue;
        }
        if (kiddo == -1) {
          kiddo = len[y];
        } else if (kiddo != len[y]) {
          okk = 0;
        }
      }
    }
    if (okk) {
      if (x != root || kiddo2 == -1) {
        len[x] = kiddo + 1;
      } else {
        len[x] = kiddo + kiddo2 + 1;
      }
    }
  }
}
int main() {
  cin.sync_with_stdio(false);
  cin >> N;
  for (int i = 1; i < N; ++i) {
    cin >> x >> y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  for (int i = 1; i <= N; ++i) {
    if (g[i].size() >= 3) {
      root = i;
    }
  }
  if (root == -1) {
    int ret = N - 1;
    while (ret % 2 == 0) ret /= 2;
    cout << ret;
    return 0;
  }
  dfs(root, -1);
  if (len[root]) {
    int ret = len[root] - 1;
    while (ret % 2 == 0) ret /= 2;
    cout << ret;
    return 0;
  }
  if (rootkids == 1) {
    while (true)
      ;
    int finlen = -1;
    int tofind = 1;
    while (g[magic].size() == 2) {
      ++tofind;
      for (auto y : g[magic]) {
        if (y != par[magic]) {
          magic = y;
        }
      }
    }
    for (auto y : g[magic]) {
      if (y == root) continue;
      if (len[y] == tofind) {
        ok = 1;
        continue;
      }
      if (len[y] == 0) {
        cout << -1;
        return 0;
      }
      if (finlen == -1) finlen = len[y];
      if (len[y] != finlen) {
        cout << -1;
        return 0;
      }
    }
    if (!ok) {
      cout << -1;
      return 0;
      ;
    }
    int ret = finlen;
    if (finlen == -1) ret = 2;
    while (ret % 2 == 0) ret /= 2;
    cout << ret;
    return 0;
  }
  if (rootkids == 2) {
    if (magic2 == 0) {
      cout << -1;
      return 0;
    }
    int tofind = len[magic2] + 1;
    int theother = -1;
    for (auto y : g[magic]) {
      if (y == par[magic]) continue;
      if (len[y] == tofind) {
        ok = 1;
        continue;
      }
      if (len[y] == 0) {
        cout << -1;
        return 0;
      }
      if (theother == -1) theother = len[y];
      if (theother != len[y]) {
        cout << -1;
        return 0;
      }
    }
    if (!ok) {
      cout << -1;
      return 0;
    }
    int ret = tofind + theother;
    while (ret % 2 == 0) {
      ret /= 2;
    }
    cout << ret;
  }
  if (rootkids > 2) {
    cout << -1;
    return 0;
  }
  return 0;
}
