sys.setrecursionlimit(10**5)

from collections import deque , Counter
from math import ceil, floor, log2 , sqrt ,lcm
import sys
from itertools import combinations ,permutations
import bisect 
mapINT = lambda: map(int, sys.stdin.readline().strip().split())
INT = lambda: int(sys.stdin.readline().strip())
LIST = lambda : list(mapINT())

# sys.setrecursionlimit(10**5)



line = []
visit = set()
n, m = mapINT()
graph = [[] for _ in range(n+1)]
def dfs(start):
  global line, graph, visit
  stack = [start]
  
  while stack:
    node = stack.pop()
    if len(graph[node]) == 2:
      a = graph[node][1]
      if a not in visit and len(graph[a]) == 2:
        visit.add(a)
        line.append(a)
        stack.append(a)
        continue
      a = graph[node][0]
      if a not in visit and len(graph[a]) == 2:
        visit.add(a)
        line.append(a)
        stack.append(a)



def solve():
  global graph
  for _ in range(m):
    v, u = mapINT()
    graph[v].append(u)
    graph[u].append(v)

  

  for i in range(n+1):
    if len(graph[i])!=2:
      graph[i] = []
    else:
      graph[i] = sorted(graph[i])

  cnt= 0
  ans =set()
  for i in range(n+1):
    line.clear()  
    if (len(graph[i])==2 and i not in visit):
      line.append(i)
      visit.add(i)
      dfs(i)
    if len(line)>2:
      if line[-1] in graph[line[0]]:
        cnt+=1      
  
  print(cnt)
  



    
t = 1
# t = INT()
for i in range(t):solve()