ice_skating.cpp

#include <bits/stdc++.h>
using namespace std;

#define rep(x, s, e) for (int x = int(s); x < int(e); ++x)

int n;
vector<bool> visited;
vector<pair<int, int>> snow;

void dfs(int cur) {
  visited[cur] = true;

  rep(i, 0, n) {
    bool canReach =
        snow[cur].first == snow[i].first || snow[cur].second == snow[i].second;
    if (canReach && !visited[i]) {
      dfs(i);
    }
  }
}

int main() {
  cin >> n;

  rep(i, 0, n) {
    int x, y;
    cin >> x >> y;
    snow.push_back({x, y});
  }

  int components = 0;
  visited.assign(n, false);
  rep(i, 0, n) {
    if (!visited[i]) {
      dfs(i);
      components++;
    }
  }

  cout << components - 1 << endl;

  return 0;
}