#!/usr/bin/python
# -*- coding: utf-8 -*-
# †
from math import sin, cos

eps = 1e-9
equal = lambda a, b: abs(a-b) < eps
greater_than = lambda a, b: a + eps > b
less_than = lambda a, b: a < b + eps

class Complex(object):
    def __init__(self, x, y): self.x, self.y = x, y
    def __add__(self, other): return Complex(self.x + other.x, self.y + other.y)
    def __sub__(self, other): return Complex(self.x - other.x, self.y - other.y)
    def __mul__(self, other):
        if type(other) is Complex:
            return Complex(self.x * other.x - self.y * other.y, self.x * other.y + other.x * self.y)
        else:
            return Complex(self.x * other, self.y * other)
    def __rmul__(self, other): return self * other
    def __div__(self, other):
        if type(other) is Complex:
            rr= other.x**2 + other.y**2
            p = (other.x * self.x + other.y * self.y) / float(rr)
            q = (other.x * self.y - other.y * self.x) / float(rr)
            return Complex(p, q)
        else:
            return Complex(self.x / float(other), self.y / float(other))
    def __eq__(self, other): return equal(self.x, other.x) and equal(self.y, other.y)
    def __ne__(self, other): return not (self == other)
    def __lt__(self, other): return self.x < other.x if self.x != other.x else self.y < other.y
    def __gt__(self, other): return self.x > other.x if self.x != other.x else self.y > other.y
    def norm(self): return self.x**2 + self.y**2
    def __abs__(self): return self.norm() ** .5
    def conjugate(self): return Complex(self.x, -self.y)
    @staticmethod
    def polar(rho, theta): return Complex(rho * cos(theta), rho * sin(theta))
    def __repr__(self):
        if equal(self.y, 0): return '{:.06f}'.format(self.x)
        if equal(self.x, 0): return '{:.06f}i'.format(self.y)
        op = '+' if self.y >= 0 else '-'
        return '{:.06f} {} {:.06f}i'.format(self.x, op, abs(self.y))

Point1 = lambda xy: Complex(*xy)
Point = Complex

def cross(p0, p1): return (p0.conjugate() * p1).y

# (ΦωΦ)＜2直線の交点
def crosspoint_ll(a0, a1, b0, b1):
    d0 = cross(b1-b0, b0-a0)
    d1 = cross(b1-b0, a1-a0)
    if equal(d0, 0) and equal(d1, 0): return a0 # 同じ直線
    if equal(d1, 0): raise '(；ω；)＜交点がないです'
    return a0 + float(d0)/d1 * (a1-a0)

pa = Point1(map(int, raw_input().split()))
pb = Point1(map(int, raw_input().split()))
pb.x *= -1
sa = Point(0, 0)
sb = Point(0, 1)
res = crosspoint_ll(pa, pb, sa, sb)
print '{:.12f}'.format(res.y)