#include <bits/stdc++.h>
#define INF 0x3f3f3f3f
#define eps 1e-5
typedef long long LL;
const double pi = acos(-1.0);
const long long mod = 25 * 1E8;
using namespace std;
const int N = 200 * 1000 + 5;
int deg[N];
bool used[N];
vector <int> g[N];
vector <int> comp;
void dfs(int v)
{
used[v] = true;
comp.push_back(v);
for(int i = 0;i < g[v].size();i++)
if(!used[g[v][i]])
dfs(g[v][i]);
}
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);
int N,M;
cin >> N >> M;
int a,b;
for(int i = 0;i < M;i++)
{
cin >> a >> b;
--a;
--b;
g[a].push_back(b);
g[b].push_back(a);
deg[a]++;
deg[b]++;
}
int ans = 0;
for(int i = 0;i < N;i++)
{
if(!used[i])
{
comp.clear();
dfs(i);
bool ok = true;
for(int j = 0;j < comp.size();j++)
ok &= (deg[comp[j]] == 2);
if(ok)
ans++;
}
}
cout << ans << endl;
return 0;
}