#include <bits/stdc++.h>
using namespace std;
vector<int> adj[200005];
int visited[200005];
int dfs(int u) {
  visited[u] = 1;
  int iscycle = ((adj[u].size() == 2) ? (1) : (0));
  for (int i = 0; i < adj[u].size(); ++i) {
    if (visited[adj[u][i]] == 0 and dfs(adj[u][i]) == 0) iscycle = 0;
  }
  return iscycle;
}
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < m; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  for (int i = 0; i <= n; ++i) visited[i] = 0;
  int ans = 0;
  for (int i = 1; i <= n; ++i)
    if (visited[i] == 0) ans += dfs(i);
  printf("%d\n", ans);
}
