/* Helloプログラム */

#include <stdio.h>
 
main()
{
	float nagasa;
	float takasa;
	float menseki;
	
	nagasa = 1.0;
	takasa = 1.0;
	
	menseki = nagasa * takasa / 2.0 ;
	
	printf("%f\n",menseki);
	
}