package Yukicoder

/**
 * Created by hichikawa on 2015/11/12.
 */
fun main(args: Array<String>) {
    fun readLineIntArray() : List<Int> {
        val str = readLine() as String
        val arrStr = str.split(" ")
        val ret = arrStr.map { it.toInt() }
        return ret
    }
    val pointX = readLineIntArray()
    val pointY = readLineIntArray()
//    println(pointX[0] + (pointY[1] - pointX[1])*pointX[1]/pointY[1].toDouble())
    println(pointX[1] + (pointY[1] - pointX[1])*pointX[0]/(pointX[0]+pointY[0]).toDouble())
}