This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
#define ve vector<int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define pi pair<int,int>
#define all(v) v.begin(),v.end()
#define si(v) (int)v.size()
#define en '\n'
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define ordered_muiltiset tree<int, null_type,less_equal<>, rb_tree_tag,tree_order_statistics_node_update>
using namespace std;
//using namespace __gnu_pbds;
typedef long long ll;
typedef unsigned long long ull;
const int N = 1e5 + 228;
const int big = 1e9;
const ll llbig = 1e18 + 228;
//ordered_set os; // os.order_of_key(4), (*os.find_by_order(5))
int n, m;
int mrk[N];
vector<int> g[N];
bool getbit(int x, int bit){
assert(bit > 0);
bit--;
return (x & (1 << bit)) == (1 << bit);
}
int main(){
cin >> n;
for (int i = 1; i <= n; i++){
int a, b; cin >> a >> b;
g[a].pb(b);
g[b].pb(a);
}
if (n <= 21){
int ans = big;
for (int mask = 1; mask <= (1 << (n + 1)); mask++){
bool ok = 1; int an = 0;
for (int i = 1; i <= n; i++) mrk[i] = 0;
for (int i = 1; i <= n; i++){
if (!getbit(mask, i)) continue;
an++;
mrk[i] = 2;
for (auto u : g[i]){
if (getbit(mask, u)) continue;
if (mrk[u]) {ok = 0; break;}
mrk[u] = 1;
}
}
for (int i = 1; i <= n; i++) {
int kol = 0;
for (auto u : g[i]){
if (getbit(mask, u)) kol++;
}
if (kol != 1) {ok = 0; break;}
}
if (ok){
ans = min(ans, an);
}
}
if (ans == big) cout << -1; else cout << ans;
}else{
assert(0);
if (n == 1){
cout << 0;
}else if (n == 2){
cout << 1;
} else cout << n - 2;
}
return 0;
}
/*
*/
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