using System;
using System.Data;
using System.Text.RegularExpressions;
class Class1{
static void Main(string[] args){
Console.WriteLine(FtoC(0));
Console.WriteLine(FtoC(40));
Console.WriteLine(FtoC(50));
Console.WriteLine(FtoC(-50));
}
public static double FtoC(double fahrenheit)
{
return ((0.5/0.9) * (fahrenheit - 32));
}
}