Thank you for posting. You can use all four characters--although the standard Korean keyboard shows 'j' and 's' as 'ㅈ' and 'ㅅ', often in handwritten Korean, people will write the former version of 'j' and 's', and people will know which character you have written regardless. So don't worry!
Cheers and please let us know if you have any other questions. Sincerely, Lyn Team KoreanClass101.com