import java.lang.*;
import java.math.*;
import java.io.*;
class CalArea
{
public static void main(String args[])
{
float a,b,c,s;
float term;
float area;
DataInputStream k;
a=0;
b=0;
c=0;
try
{
k=new DataInputStream(System.in);
System.out.println("Enter a:");
a=Float.parseFloat(k.readLine());
System.out.println("Enter b:");
b=Float.parseFloat(k.readLine());
System.out.println("Enter c:");
c=Float.parseFloat(k.readLine());
}
catch(NumberFormatException e)
{
a=5;
b=5;
c=5;
}
catch(Exception e)
{
System.out.println("ERROR!");
}
s=(a+b+c)/2;
term=s*(s-a)*(s-b)*(s-c);
if(term<=0)
{
System.out.println("INVALID PARAMETERS!");
}
else
{
area=(float)Math.sqrt(term);
System.out.println("Area="+area);
}
}
}