#include <bits/stdc++.h>

using namespace std;

struct node {
	node(long long xi, long long yi):x(xi) {
		y.insert(yi);
	}
	long long x;
	mutable set <long long>y;
	long long operator < (node a) const{
		return x < a.x;
	}
};

int main () {
	ios::sync_with_stdio(false);
	
	set < node > graph;
	
	long long n;
	
	while ( cin >> n ) {
long long m = 0;
		for ( long long j = 0; j < n; ++j ) {
			long long x, y;
			
			cin >> x >> y;
			 auto i = graph.find(node(x,0)) ;
			if ( i == graph.end() ) {
				graph.insert(node(x, y));		
			} else {
				i -> y.insert(y);
			}
		}
		
		for ( auto i : graph ) {
			if ( i . y.size() == 1 )
				continue; 
			for ( set<long long>::iterator j = i.y.begin(); j != i.y.end(); ++j ) {
				for ( set<long long>::iterator k = j; k != i . y.end(); ++k ) {
					long long dif = *k - *j;
					node tmp(i . x + dif, 0);
					set<node>::iterator right = graph.find(tmp);
					if ( right -> x <= i.x )
						continue;
					if ( right -> y.find(*k) != right -> y.end() && 
						right -> y.find(*j) != right -> y.end() ) { 
						m = max ( m , dif );
					}
				
				}				
			}
		
		}
	
		cout << m << endl;

	}
	return 0;
}