#!/usr/bin/env python3
import sys

def main():
    N, M = map(int, input().split())
    box = [[] for _ in range(M)]
    color = [[] for _ in range(N)]
    B, C = [], []
    for i in range(N):
        bb, cc = map(lambda i: int(i) - 1, input().split())
        box[bb].append(i)
        color[cc].append(i)
        B.append(bb)
        C.append(cc)
    from collections import defaultdict

    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 0

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

            self.parents[x] += self.parents[y]
            self.parents[y] = x
            return 1

        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 < 0]

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

        def all_group_members(self):
            group_members = defaultdict(list)
            for member in range(self.n):
                group_members[self.find(member)].append(member)
            return group_members

        def __str__(self):
            return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())
    uf = UnionFind(N)
    ans = 0
    for i in range(M):
        for j in range(len(box[i]) - 1):
            # print(box[i][j] + 1, box[i][j + 1] + 1)
            uf.union(box[i][j], box[i][j + 1])
    # print("---")
    for i in range(N):
        for j in range(len(color[i]) - 1):
            # print(color[i][j] + 1, color[i][j + 1] + 1)
            ans += uf.union(color[i][j], color[i][j + 1])
    # print(uf)
    print(ans)

    return

if __name__ == '__main__':
    main()