#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define Foxyy cin.tie(0); cout.sync_with_stdio(0); cout.tie(0);
const int INF = 0x3f3f3f3f;
struct Solver {
int& n;
vector<vector<int>>& adj;
void solve() {
int ans = INF;
for (int mask = 2; mask < (1 << n); mask++) {
if (__builtin_popcount(mask) % 2 != 0) continue;
bool valid = true;
for (int i = 0; i < n; i++) {
int cnt = 0;
for (int j : adj[i]) if ((mask >> j) & 1) {
cnt++;
}
if (cnt != 1) {
valid = false;
break;
}
}
if (valid) {
ans = min(ans, __builtin_popcount(mask));
}
}
if (ans == INF) {
cout << "-1\n";
} else {
cout << ans << '\n';
}
}
};
signed main() {
Foxyy
int T = 1;
// cin >> T;
while(T--) {
int n;
cin >> n;
vector<vector<int>> adj(n);
for (int i = 0; i < n; i++) {
int a, b;
cin >> a >> b;
a--, b--;
adj[a].push_back(b);
adj[b].push_back(a);
}
Solver solver{n, adj};
solver.solve();
}
}
