{$APPTYPECONSOLE}
var
  a, b, c, d, sum: double;
  function square(a, b, c: double):double;
    var
      p: double;
    begin
      if (a + b <= c) or (b + c <= a) or (a + c <= b) then begin
        writeln (‘There is no such triangle’);
        halt (0);
      end;
      p := (a + b + c) / 2;
      result := sqrt (p * (p - a) * (p - b) * (p - c));
    end;
  begin
    readln(a, b, c, d);
    sum := square (1, 2, a) + square (2, 2.5, b) + square(2.5, c, d);
    writeln (sum);
    readln;
    readln;
  end;