/* Heron's formula
*/

import java.io.*;

public class Heron {
	
	
	public static void main (String [] args) throws IOException {

		DataInput keyboard = new DataInputStream(System.in);
		String 	strA,
				strB,
				strC;	// used to input the sides
		double	sideA,	// length of sides
				sideB,
				sideC,
				halfP,	// half perimeter
				area;
			
		System.out.print ("Enter Side A: -->");	
		strA = keyboard.readLine();
		sideA = Double.parseDouble(strA);
	
		System.out.print ("Enter Side B: -->");	
		strB = keyboard.readLine();
		sideB = Double.parseDouble(strB);
	
		System.out.print ("Enter Side C: -->");	
		strC = keyboard.readLine();
		sideC = Double.parseDouble(strC);
	
		halfP = ( sideA + sideB + sideC ) / 2;
		if (halfP <= sideA || halfP <= sideB || halfP <= sideC)
			System.out.println ("Not a triangle!");
		else {
			area = Math.sqrt(halfP*(halfP-sideA)*(halfP-sideB)*(halfP-sideC));
			System.out.println ("Area is " + area );	
		}
			
	} //main
	
	
}// class