#include <cstdio>
#include <vector>
// #include <algorithm>
// #include <utility>

#define ULL unsigned long long
#define LL long long
#define uint unsigned int

std::vector<std::vector<uint>> g;
std::vector<bool> used;

bool dfs(uint v) {
  used[v] = true;
  if (g[v].size() != 2) {
    return false;
  }
  for (uint u : g[v]) {
    if (used[u] == false) {
      dfs(u);
    }
  }
  return true;
}

int main(void) {
  uint n, m, cycles = 0;
  scanf("%u %u", &n, &m);
  g.resize(m);
  used.resize(n);
  //
  // printf("%u\n", n);

  // for (uint i = 0; i < n; i++) {
  // }
  uint v, u;
  for (uint i = 0; i < m; i++) {
    scanf("%u %u", &v, &u);
    g[v].push_back(u);
    g[u].push_back(v);
  }
  for (uint i = 0; i < n; i++) {
    if (!used[i]) {
      if (dfs(i)) {
        cycles++;
      }
    }
  }

  printf("%u\n", cycles);

  return 0;
}