#include <bits/stdc++.h>   using namespace std;   const int MAX = 200200;   vector<int> adj[MAX];   int ch[MAX], sz, from[MAX], dpthMx[MAX], dpthMn[MAX], n;   void dfs(int cur, int par) {     for (auto i : adj[cur])       if (i != par) {         dfs(i, cur);         dpthMn[cur] = min(dpthMn[cur], dpthMn[i] + 1);         dpthMx[cur] = max(dpthMx[cur], dpthMx[i] + 1);       }     if (dpthMn[cur] == MAX) dpthMn[cur] = 0;   }   pair<int, int> dfs0(int cur, int par, int d) {     from[cur] = par;     pair<int, int> ret(d, cur);     for (auto i : adj[cur])       if (i != par) ret = max(ret, dfs0(i, cur, d + 1));     return ret;   }   int main() {     scanf( %d , &n);     fill(dpthMn, dpthMn + n + 1, MAX);     for (int i = 1, u, v; i < n; ++i) {       scanf( %d%d , &u, &v);       adj[u].push_back(v);       adj[v].push_back(u);     }     pair<int, int> diam = dfs0(dfs0(1, 0, 0).second, 0, 0);     while (diam.first > 0) diam.first -= 2, diam.second = from[diam.second];     dfs(diam.second, 0);     for (auto i : adj[diam.second]) {       if (dpthMx[i] != dpthMn[i]) return puts( -1 ), 0;       ch[sz++] = dpthMx[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;   }   