#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;
using u128 = unsigned __int128;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    std::cout << std::fixed << std::setprecision(10);
    
    int n;
    std::cin >> n;
    
    double ans = INFINITY;
    
    for (int i = 0; i < n; i++) {
        int x1, y1, x2, y2;
        std::cin >> x1 >> y1 >> x2 >> y2;
        
        if (x1 > x2) {
            std::swap(x1, x2);
            std::swap(y1, y2);
        }
        
        if (x1 < 0 && x2 > 0) {
            double y = double(x2 * y1 - x1 * y2) / (x2 - x1);
            if (y > 0) {
                ans = std::min(ans, y);
            }
        }
    }
    
    if (ans == INFINITY) {
        ans = -1;
    }
    
    std::cout << ans << "\n";
    
    return 0;
}