class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            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 x == y:
            return

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

        self.parents[x] += self.parents[y]
        self.parents[y] = x

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

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

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

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

    def groups(self):
        roots = self.roots()
        r_to_g = {}
        for i, r in enumerate(roots):
            r_to_g[r] = i
        groups = [[] for _ in roots]
        for i in range(self.n):
            groups[r_to_g[self.find(i)]].append(i)
        return groups


n, m = map(int, input().split())

G = [set() for _ in range(n)]
for i in range(n):
    b, c = map(int, input().split())
    b -= 1
    c -= 1
    G[c].add(b)

uf = UnionFind(n)
G = [list(g) for g in G]
res = 0
for g in G:
    for i in range(len(g)-1):
        if uf.same(g[i],g[i+1]):
            continue
        uf.union(g[i],g[i+1])
        res += 1

print(res)