#include <bits/stdc++.h>
using namespace std;
#define int long long
const int modulo = 1e9+7;
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<vector<int>> adj(n+1);
for(int i=1;i<=n;i++){
int a,b;
cin >> a >> b;
adj[a].emplace_back(b);
adj[b].emplace_back(a);
}
auto solve = [&](int b1,int b2){
vector<int> myLevel(n+1);
vector<int> ans(4);
vector<bool> allowed(4,true);
function<void(int,int,int)> dfs = [&](int x,int p,int level){
ans[level]++;
myLevel[x]=level;
int children = 0;
for(int&i:adj[x])if(i!=p){
if(i==b1 and x==b2)continue;
if(i==b2 and x==b1)continue;
children++;
dfs(i,x,(level+1)&3);
}
if(children==0)allowed[(level+1)&3]=false;
};
dfs(1,0,0);
allowed[2]=false;
allowed[myLevel[b1]]=false;
allowed[myLevel[b2]]=false;
allowed[myLevel[(b1+3)&3]]=false;
allowed[myLevel[(b2+3)&3]]=false;
int anss = 1e9;
for(int i=0;i<4;i++)if(allowed[i])anss=min(anss,ans[i]+ans[(i+1)&3]);
return anss;
};
vector<bool> visited(n+1);
vector<int> par(n+1);
vector<pair<int,int>> edges;
function<void(int,int)> dfs = [&](int x,int p){
visited[x]=true;
par[x]=p;
for(int&i:adj[x])if(i!=p){
if(visited[i]){
if(!edges.empty())continue;
edges.emplace_back(x,p);
edges.emplace_back(par[p],p);
edges.emplace_back(x,i);
continue;
}
dfs(i,x);
}
};
dfs(1,0);
int anss = 1e9;
for(auto&[a,b]:edges)anss=min(anss,solve(a,b));
if(anss==1e9)cout<<"-1\n";
else cout << anss << '\n';
}
