using System;
using System.Collections.Generic;
using System.Linq;

namespace yukicoder
{
    public class Program
    {
        public static void Main()
        {
            var line = Console.ReadLine().Split();
            var xa = -double.Parse(line[0]);
            var ya = double.Parse(line[1]);
            line = Console.ReadLine().Split();
            var xb = double.Parse(line[0]);
            var yb = double.Parse(line[1]);
            Console.WriteLine(-xa * (yb - ya) / (xb - xa) + ya);
        }
    }
}