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CyclicComponents.cpp
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CyclicComponents.cpp
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/*
Author: Sanskar Agarwal
Nick: sanskaragarwal
Birla Institute Of Technology, Mesra
*/
#include <bits/stdc++.h>
using namespace std;
#define ll long long int
#define endl "\n"
#define fast ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define F(i,a,b) for(ll i = (ll)(a); i <= (ll)(b); i++)
#define RF(i,a,b) for(ll i = (ll)(a); i >= (ll)(b); i--)
#define INF 100009
#define mod 1000000007
#define pb(x) push_back(x)
#define mp(x,y) make_pair(x,y)
#define ff first
#define ss second
const int N = 200 * 1000 + 11;
int n, m;
int deg[N];
bool used[N];
vector<int> comp;
vector<int> g[N];
void dfs(int v)
{
used[v] = true;
comp.push_back(v);
for (auto to : g[v])
if (!used[to])
dfs(to);
}
int main()
{
fast
cin>>n>>m;
for (int i = 0; i < m; ++i)
{
int x, y;
cin>>x>>y;
--x, --y;
g[x].push_back(y);
g[y].push_back(x);
++deg[x];
++deg[y];
}
int ans = 0;
for (int i = 0; i < n; ++i)
{
if (!used[i])
{
comp.clear();
dfs(i);
bool ok = true;
for (auto v : comp) ok &= deg[v] == 2;
if (ok) ++ans;
}
}
cout<<ans<<endl;
return 0;
}