/**********************************************************************************/
/*  Problem: d489 "伏林的三角地" from 板橋高中                          */
/*  Language: JAVA (548 Bytes)                                                    */
/*  Result: AC(97ms, 2.4MB) judge by this@ZeroJudge                               */
/*  Author: ssc24 at 2011-09-26 12:26:28                                          */
/**********************************************************************************/


package javaapplication42;
import java.util.*;
import java.math.*;



public class JavaApplication42 {


  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    while (sc.hasNext()){

        int a =sc.nextInt();
        int b =sc.nextInt();
        int c =sc.nextInt();
        double s =((a+b+c)*0.5);
        //int price =(s*(s-a)*(s-b)*(s-c)); // 求面積需要開根號
        System.out.printf("%.0f%n",(s*(s-a)*(s-b)*(s-c)));


    }//whlle*/
  }//main

}//class