I'm not sure if you've checked these reviews yet:
Math 1F03,
1M03, and I'm guessing you mean
1LS3?
I think the course you should take should depend on how much
math you've taken. For e.g. you can't take
1F03 if you have Calculus and Vectors (12 U). So before you take 1LS3 or 1M03, you'd need the credit for
1F03.