from collections import deque
N,M = map(int,input().split())
G = {i:[] for i in range(1,N+M+1)}
for _ in range(N):
    b,c = map(int,input().split())
    G[b].append(M+c)
    G[M+c].append(b)
col = [-1]*(N+M+1)
cur = 0
for i in range(1,N+M+1):
    if col[i]<0:
        col[i] = cur
        que = deque([i])
        while que:
            j = que.popleft()
            for k in G[j]:
                if col[k]<0:
                    col[k] = cur
                    que.append(k)
        cur += 1
cnt = set()
for i in range(1,M+1):
    cnt.add(col[i])
print(M-len(cnt))