#include
#include
int main()
{
double a, b, c, p, s;
printf("請(qǐng)輸入三角形的三邊長(zhǎng):");
scanf("%lf%lf%lf", &a, &b, &c);
p = (a+b+c)/2;
s = sqrt( p*(p-a)*(p-b)*(p-c));
printf("%.3f\n", s);
return 0;
}