n, m = map(int, input().split())

from collections import deque

#色iのスライムがどの箱に入っているかを管理
color = [[] for _ in range(n+1)]
#箱iにどの色のスライムが入っているかを管理 
box = [[] for _ in range(m+1)]

for i in range(n):
  b, c = map(int, input().split())
  box[b].append(c)
  color[c].append(b)

#アクセス済みの箱を管理
dist = [-1] * (m+1)
dist[0] = 0

ans = 0

for i in range(m+1):
  if dist[i] == -1:
    dist[i] = 0
    d = deque()
    d.append(i)
    while d:
      v = d.popleft()
      for j in box[v]:
        for k in color[j]:
          if dist[k] != -1:
            continue
          dist[k] = dist[v] + 1
          d.append(k)
          ans += 1

print(ans)