n, m = map(int, input().split())
box = [[]for _ in range(m+1)]
color = [[]for _ in range(n+1)]
for _ in range(n):
  b, c = map(int, input().split())
  box[b].append(c)
  color[c].append(b)

boxused = [-1]*(m+1)
boxused[0]= 0
colorused = [-1]*(n+1)
colorused[0] = 0

from collections import deque

cnt = 0
for i in range(m+1):
  if boxused[i] == -1:
    d = deque()
    d.append(i)
    boxused[i] = 0
    while d:
      v = d.popleft()
      for x in box[v]:
        if colorused[x] == -1:
          colorused[x] = 0
          for y in color[x]:
            if boxused[y] == -1:
              boxused[y] = 0
              d.append(y)
              cnt += 1

print(cnt)