class Unionfind:
     
    def __init__(self,n):
        self.uf = [-1]*n
 
    def find(self,x):
        if self.uf[x] < 0:
            return x
        else:
            self.uf[x] = self.find(self.uf[x])
            return self.uf[x]
 
    def same(self,x,y):
        return self.find(x) == self.find(y)
 
    def union(self,x,y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return False
        if self.uf[x] > self.uf[y]:
            x,y = y,x
        self.uf[x] += self.uf[y]
        self.uf[y] = x
        return True
 
    def size(self,x):
        x = self.find(x)
        return -self.uf[x]

n,m = map(int,input().split())
l = [set() for i in range(n+1)]
for i in range(n):
    b,c = map(int,input().split())
    l[c].add(b)

uf = Unionfind(m+1)
ans = 0
for i in range(1,n+1):
    if len(l[i]) < 2:
        continue
    now = list(l[i])
    for i,j in zip(now,now[1:]):
        if uf.same(i,j):
            continue
        uf.union(i,j)
        ans += 1
print(ans)