#include <iostream>
#include <map>

using namespace std;


int main()
{
    size_t n = 0;

    while (cin >> n) {

	map<pair<size_t,size_t>, size_t> mpi;
	size_t maxX = 0;
	size_t maxY = 0;

	for (size_t i=0; i<n; ++i) {
	    size_t x, y;
	    cin >> x >> y;
    	    mpi[pair<size_t, size_t>(x, y)]=0;
    	    if (x > maxX) maxX = x;
    	    if (y > maxY) maxY = y;
	}

while (true) {

	size_t max = 0;
	size_t val = 0;
	
	for (auto& pi : mpi) {
//	    //cout << "* pi(" << pi.first.first << "," << pi.first.second << ")\n";
	    if (!val) val = pi.second;

	    pair<size_t, size_t> p[4];
	    p[0] = pair<size_t, size_t>(pi.first.first-1,pi.first.second);
	    p[1] = pair<size_t, size_t>(pi.first.first+1,pi.first.second);
	    p[2] = pair<size_t, size_t>(pi.first.first,pi.first.second-1);
	    p[3] = pair<size_t, size_t>(pi.first.first,pi.first.second+1);

	    for (size_t q = 0; q < 4; ++q) {
//		//cout << "p["<< p[q].first << "," <<  p[q].second << "]\n";
		if (mpi.count(p[q])) {
			bool empty = pi.second == 0;
    			++pi.second;
			if (!empty && mpi[p[q]] == 0) { mpi[p[q]] = 1; if (max == 0) max = 1; }
			if (pi.second > max) max = pi.second;
		}
	    }
	}

	if (!max) break;

	map<pair<size_t,size_t>, size_t>::iterator it = mpi.begin();

	for (; it != mpi.end();) {
	    //cout << "(" << it->first.first << "," << it->first.second << ")" << it->second;
	    if (max && it->second == max) {
		 it = mpi.erase(it);
		 //cout << "x\n";
		 max = 0;
	    } else { 
		it->second = 0;
		++it;
		//cout << "*\n";
	    }
	}
}

	cout << mpi.size() << "\n";
    }
    return 0;
}