#include <bits/stdc++.h>
using namespace std;
#define int long long
const int modulo = 1e9+7;
const int INF = 1e9;
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<array<int,4>(int,int)> dfs = [&](int x,int p){
array<int,4> DP = {0,0,1,1};
int minima = INF;
int minima2 = INF;
for(int&i:adj[x])if(i!=p){
if(i==b1 and x==b2)continue;
if(i==b2 and x==b1)continue;
auto res = dfs(i,x);
DP[0]+=res[1];
DP[1]+=res[1];
DP[2]+=res[0];
DP[3]+=res[0];
minima=min(minima,res[2]-res[1]);
minima2=min(minima2,res[3]-res[0]);
}
DP[1]+=minima;
DP[2]+=minima2;
if(x==b1 or x==b2)DP[2]=DP[3]=INF;
return DP;
};
return min(dfs(1,0)[1],dfs(1,0)[2]);
};
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>n)cout<<"-1\n";
else cout << anss << '\n';
}
