N,M=map(int,input().split())
l=[[] for i in range(N)]
for i in range(N):
    b,c=map(int,input().split())
    b-=1
    c-=1
    l[c].append(b)
root=[i for i in range(M)]
height=[0]*M
def find(a):
    f=a
    if a==root[a]:
        return a
    while a!=root[a]:
        a=root[a]
    root[f]=a
    return a
def union(a,b):
    A=find(a)
    B=find(b)
    if A==B:
        return 0
    if height[A]>height[B]:
        root[B]=root[A]
        return 1
    else:
        root[A]=root[B]
        if height[A]==height[B]:
            height[B]+=1
        return 1
ans=0
for i in l:
    if len(i)<2:
        continue
    S=i[0]
    for j in range(1,len(i)):
        ans+=union(i[j],S)
print(ans)