import sys
input = sys.stdin.readline

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

XY=[list(map(int,input().split())) for i in range(N)]

LIST=[]
for x,y in XY:
    LIST.append(x)
    LIST.append(y)

LIST=sorted(set(LIST))
D={LIST[i]:i for i in range(len(LIST))}

for i in range(N):
    XY[i][0]=D[XY[i][0]]
    XY[i][1]=D[XY[i][1]]

# UnionFind

Group = [i for i in range(len(LIST)+1)] # グループ分け
Nodes = [1]*(len(LIST)+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)

for x,y in XY:
    Union(x,y)

A=[0]*len(LIST)
for x,y in XY:
    A[find(x)]+=1

ANS=0

for i in range(len(LIST)):
    if find(i)==i:
        ANS+=min(A[i],Nodes[i])

print(ANS)