Problem:
Celsius/Fahrenheit

　

In Japan, temperature is usually expressed using the Celsius (℃) scale. In America, they used the Fahrenheit (℉) scale instead. $20$ degrees Celsius is roughly equal to $68$ degrees Fahrenheit. A phrase such as "Today’s temperature is $68$ degrees" is commonly encountered while you are in America.

A value in Fahrenheit can be converted to Celsius by first subtracting $32$ and then multiplying by $\frac{5}{9}$. A simplified method may be used to produce a rough estimate: first subtract $30$ and then divide by $2$. Using the latter method, $68$ Fahrenheit is converted to $19$ Centigrade, i.e., $\frac{(68-30)}{2}$.

Make a program to convert Fahrenheit to Celsius using the simplified method: $C = \frac{F - 30}{2}$.

Input

The input is given in the following format.

$F$

The input line provides a temperature in Fahrenheit $F$ ($30 \leq F \leq 100$), which is an integer divisible by $2$.

Output

Output the converted Celsius temperature in a line.

Sample Input 1

68

Sample Output 1

19

Sample Input 2

50

Sample Output 2

10

Solution in C# (judge verdict: Accepted)

using System;

public class hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        Console.WriteLine((n - 30) / 2);
    }
}