let inpt = readLine()!.split(separator: " ").map({Double($0)!})

var needTea = inpt[1] * inpt[2] / inpt[0]
var needCoffie = inpt[2]

if(needTea > inpt[3]) {
    needTea = inpt[3]
    needCoffie = inpt[0] * inpt[3] / inpt[1]
}

print(needTea + needCoffie)