program ger;
uses crt;
var a, b, c:integer;
function geron(a,b,c:integer):double;
var p:double;
begin
      p:=(a+b+c)/2;
      geron:=p*(p-a)*(p-b)*(p-c);
end;
begin
      write('vvedite a-> '); readln(a);
      write('vvedite b-> '); readln(b);
      write('vvedite c-> '); readln(c);
      writeln(geron(a,b,c));
      readkey;
end.