#include <iostream>
#include <vector>
#include <iomanip>
#include <limits>

// t = x2 / (x2-x1)
// y = (y1 * x2 + y2 * -x1) / (x2 - x1)


int main()
{
    int n;
    std::cin >> n;
    std::vector<int> x1(n);
    std::vector<int> y1(n);
    std::vector<int> x2(n);
    std::vector<int> y2(n);
    for(int i=0; i<n; i++)
    {
        std::cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
        if(x1[i] > x2[i])
        {
            std::swap(x1[i], x2[i]);
            std::swap(y1[i], y2[i]);
        }
    }

    double maxy = std::numeric_limits<double>::infinity();
    
    for(int i=0; i<n; i++)
    {
        if(x1[i] > 0 || x2[i] < 0)
            continue;
            
        double t = double(x2[i]) / double(x2[i]-x1[i]);
        double y = double(y1[i]) * t + double(y2[i]) * (1-t);
        if(y < 0)
            continue;
        maxy = std::min(maxy, y);
    }
    if(maxy == std::numeric_limits<double>::infinity())
        std::cout << "-1.0" << std::endl;
    else
        std::cout << std::setprecision(30) << maxy << std::endl;
}