#include <iostream>
#include <cmath>
#include <stdexcept>
using
namespace
std;
double
area(
double
a,
double
b,
double
c) {
if
(a <= 0 || b <= 0 || c <= 0)
throw
invalid_argument(
"the side length should be positive"
);
if
(a + b <= c || b + c <= a || c + a <= b)
throw
invalid_argument(
"the side length should fit the triangle inequality"
);
double
s = (a + b + c) / 2;
return
sqrt
(s * (s - a) * (s - b) * (s - c));
}
int
main() {
double
a, b, c;cin >> a >> b >> c;
try
{
double
s = area(a, b, c);
cout <<
"Area: "
<< s << endl;
}
catch
(exception &e) {
cout <<
"Error: "
<< e.what() << endl;
}
}