#include <bits/stdc++.h>
using namespace std;
#define pb push_back
using pr = pair<int, int>;
const int INF = 1e9+7, MOD = 1e9+7;
int n;
vector<vector<int>> edge;
vector<int> three, more;
set<int> only;
bool no = 0;
bitset<1000000> crit;
void insert(int A) {
if (edge[A].size() == 3) {
if (!only.empty()) {
only.insert(A);
for (auto i : edge[A]) {
only.insert(i);
}
}
else {
set<int> nonly;
if (only.count(A)) nonly.insert(A);
for (auto i : edge[A]) {
if (only.count(i)) {
nonly.insert(i);
}
}
if (nonly.empty()) {
no = 1;
}
only = nonly;
}
}
if (edge[A].size() > 3) {
set<int> nonly;
if (only.count(A)) {
nonly.insert(A);
}
else {
no = 1;
}
only = nonly;
}
}
void Init(int N_) {
n = N_;
edge.resize(n);
}
void Link(int A, int B) {
edge[A].pb(B);
edge[B].pb(A);
if (no) return;
insert(A);
insert(B);
}
int CountCritical() {
if (no) return 0;
if (only.empty()) return n;
return only.size();
}
