/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int sum = 0;
		for (int i = 2; i < 31; i++){
			if (i % 2 == 0)
				sum++;
			else
				sum+=2;
		}
		System.out.println(sum);
	}

}