import sys
input = sys.stdin.readline

N,M=map(int,input().split())

# UnionFind

Group = [i for i in range(M+1)] # グループ分け
Nodes = [1]*(M+1) # 各グループのノードの数

def find(x):
    while Group[x] != x:
        x=Group[x]
    return x

def Union(x,y):
    if find(x) != find(y):
        if Nodes[find(x)] < Nodes[find(y)]:
            
            Nodes[find(y)] += Nodes[find(x)]
            Nodes[find(x)] = 0
            Group[find(x)] = find(y)
            
        else:
            Nodes[find(x)] += Nodes[find(y)]
            Nodes[find(y)] = 0
            Group[find(y)] = find(x)

C=[[] for i in range(N+1)]
for i in range(N):
    b,c=map(int,input().split())
    C[c].append(b)

for i in range(N+1):
    for j in range(len(C[i])-1):
        Union(C[i][j],C[i][j+1])

ANS=0

for i in range(M+1):
    if i!=find(i):
        ANS+=1

print(ANS)