C :

#include<stdio.h>
#include<math.h>
int main()
{
	int a, b, c;
	double s;
	scanf("%d%d%d", &a, &b, &c);
	if ((a + b) > c && ((a + c) > b) && ((b + c) > a))
	{
		s = (0.25)*sqrt((a + b + c)*(a + b - c)*(a + c - b)*(b + c - a));
		printf("%.2lf\n", s);
	}
	else
	{
		printf("Can't\n");
	}
	return 0;
}

Pascal :

var
a,b,c,h,s:real;
t:string;
begin
readln(a,b,c);
if (a+b>c)and(b+c>a)and(a+c>b) then
  begin
  s:=a*b/2;
writeln(s:0:2);
end
  else writeln('Can''','t');
end.