/* 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
	{
		double khWert=7;
		double phWert = 7;
		double co2Ergebnis=Math.floor((7.90+Math.log(khWert/(2.8*phWert))/Math.log(10))*100)/100;
		System.out.print(co2Ergebnis);
 
		// your code goes here
	}
}

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