var
   x, n : integer;

begin
   readLn(n);
   if n mod 10 = 7 then dec(n);
   x := 3 * n div 10;
   writeLn(x);
end.

with this code WA#48;
pls!!! help!!!
   var
     x, n : integer;

begin
  readLn(n);
  if n mod 10 = 7 then x := TRUNC((n - 1) * ln(2)/ln(10))
  else x := TRUNC(n * ln(2)/ln(10));
  writeLn(x);
end.