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

typedef long long ll;

int main() {
  ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  int n; cin>>n;
  vector<int> x1(n), y1(n), x2(n), y2(n);
  for (int i=0; i<n; i++) {
    cin>>x1[i]>>y1[i]>>x2[i]>>y2[i];
    if(x1[i]>x2[i]) swap(x1[i],x2[i]), swap(y1[i],y2[i]);
  }
  ll top=1, bot=0;
  for (int i=0; i<n; i++) {
    if(x1[i]>0||x2[i]<0) continue;
    ll top2=y1[i]*x2[i]-y2[i]*x1[i];
    ll bot2=x2[i]-x1[i];
    if(top2<0) continue;
    if(top2*bot-bot2*top<0)
      top=top2, bot=bot2;
  }
  cout<<setprecision(30)<<fixed<<(bot ? double(top)/bot : -1.0)<<"\n";
  return 0;
}