var a, b, c, p: real;
begin
readln(a, b, c);
p:= (a + b + c) / 2;
writeln(sqrt(p * (p - a) * (p - b) * (p - c)));
end.
/////////////////////////////////
var num1, num2: real;
begin
randomize;
num1:= random(1, 100);
num2:= random(1, 100);
writeln(num1);
writeln(num2);
writeln(num1 + num2);
end.
/////////////////////////////////
var num: real;
begin
randomize;
num:= random(10, 99);
writeln((num div 10) + (num mod 10)); // Сумма
writeln((num div 10) * (num mod 10)); // Произведение
writeln((num div 10) + (num mod 10) * 10); // ~ab = ~ba
end.