#include<bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include"debug.h"
#else
#define debug(...) void()
#endif
#define all(x) (x).begin(),(x).end()
template<class T>
auto ary(T *a,int l,int r){
	return vector<T>{a+l,a+1+r};
}
using ll=long long;
using ull=unsigned ll;
int n,p,q;
ll a,b,c;
void ins(ll x,ll y){
	for(;x;swap(a,x),swap(b,y)){
		ll t=a/x;
		a-=x*t,b-=y*t;
	}
	c=__gcd(c,y);
	if(c)b%=c;
}
int main(){
	scanf("%d%d%d",&n,&p,&q);
	for(int x,y,i=2;i<=n;i++){
		scanf("%d%d",&x,&y);
		ins(x-p,y-q);
	}
	if(!c)puts("-1");
	else cout<<abs(a*c)<<endl;
	return 0;
}
#ifdef DEBUG
#include"debug.hpp"
#endif