import sys
input = lambda : sys.stdin.readline().rstrip()

sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")

class UF:
    # unionfind
    def __init__(self, n):
        self.n = n
        self.parent = list(range(n))
        self.size = [1] * n
    def root(self, i):
        inter = set()
        while self.parent[i]!=i:
            inter.add(i)
            i = self.parent[i]
        r = i
        for i in inter:
            self.parent[i] = r
        return r
    def connect(self, i, j):
        # 繋いだかどうかを返す
        ri = self.root(i)
        rj = self.root(j)
        if ri==rj:
            return False
        if self.size[ri]<self.size[rj]:
            self.parent[ri] = rj
            self.size[rj] += self.size[ri]
        else:
            self.parent[rj] = ri
            self.size[ri] += self.size[rj]
        return True

n,m = list(map(int, input().split()))
cs = [[] for _ in range(n)]
for i in range(n):
    b,c = map(int, input().split())
    b -= 1
    c -= 1
    cs[c].append(b)
#     cs[b].append(c)
uf = UF(m)
ans = 0
for c in range(n):
    if not cs[c]:
        continue
    b0 = cs[c][0]
    for b in cs[c]:
        if uf.connect(b,b0):
            ans += 1
print(ans)