1038

    # include <stdio.h>
    # include <math.h>
    # include <string.h>
    # define S(a,b,c) S=(a+b+c)/2
    # define area(S,a,b,c) area=sqrt(S*(S-a)*(S-b)*(S-c))
    main()
    {
    	float a,b,c,S,area;
    	scanf("%f %f %f",&a,&b,&c);
    	S(a,b,c);
    	area(S,a,b,c);
    	printf("%.3f",area);
    }