/*
In the name of Allah
made by: Ahmed_Solyman
*/
#include <bits/stdc++.h>
#include <ext/rope>
using namespace std;
using namespace __gnu_cxx;
#pragma GCC optimize("-Ofast")
#pragma GCC optimize("-O1")
//-------------------------------------------------------------//
typedef long long ll;
typedef unsigned long long ull;
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define PI acos(-1)
#define lb lower_bound
#define ub upper_bound
#define endl '\n'
#define all(v) v.begin(),v.end()
#define allr(v) v.rbegin(),v.rend()
#define sum_to(n) (n*(n+1))/2
#define pb push_back
#define pf push_front
#define fil(arr,x) memset(arr,x,sizeof(arr))
const ll mod=1e9+7;
int dx[8]={0,1,0,-1,1,1,-1,-1};
int dy[8]={1,0,-1,0,1,-1,-1,1};
//-------------------------------------------------------------//
ll lcm(ll a,ll b)
{
return (max(a,b)/__gcd(a,b))*min(a,b);
}
void person_bool(bool x)
{
cout<<(x?"YES":"NO")<<endl;
}
int main()
{
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
#ifndef ONLINE_JUDGE
//freopen("input.in", "r", stdin);
//freopen("output.out", "w", stdout);
#endif
fast
int n;cin>>n;
vector<int>adj[n];
int deg[n];
for(int i=0;i<n;i++){
int u,v;cin>>u>>v;u--;v--;
deg[u]++;deg[v]++;
adj[u].push_back(v);
adj[v].push_back(u);
}
bool ok=1;
for(int i=0;i<n;i++)ok&=(deg[i]==2);
if(ok){
if(n%4)cout<<-1<<endl;
else cout<<n/2<<endl;
return 0;
}
int ans=-1;
for(int i=1;i<(1<<n);i++){
vector<bool>v(n);
for(int j=0;j<n;j++){
if((1<<j)&i){
v[j]=1;
}
}
bool valid=1;
for(int j=0;j<n;j++){
int cnt=0;
for(auto ch:adj[j]){
if(v[ch])cnt++;
}
valid&=(cnt==1);
}
if(valid){
if(ans==-1){
ans=__builtin_popcount(i);
}
else{
ans=min(ans,__builtin_popcount(i));
}
}
}
cout<<ans<<endl;
return 0;
}
