#unionfind経路圧縮あり
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = list(range(n))

    def find(self, x):
        if self.parents[x] == x:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if self.parents[x] > self.parents[y]:
            x, y = y, x
            
        if x == y:
            return

        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x == i]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N,M = map(int,input().split())
lsN = [[] for i in range(N)]
for i in range(N):
    b,c = map(int,input().split())
    b -= 1
    c -= 1
    lsN[c].append(b)
#合わせるunionfind,unionした回数
UF = UnionFind(M)
ans = 0
for i in range(N):
    if len(lsN[i]) <= 1:
        continue
    
    for j in range(len(lsN[i])-1):
        if UF.find(lsN[i][j]) == UF.find(lsN[i][j+1]):
            continue
        ans += 1
        UF.union(lsN[i][j],lsN[i][j+1])
print(ans)